I'm posting this in response to your PM. I tried to attach a .doc file because it's such a long post, but this is the only way I guess, as I don't have your email. A disclaimer, there are many ways to do this, but this is how I would do it.
I don’t know how much you know about this, and don’t want to sound as if I’m talking “down” to you. However, I think I need to be as detailed as possible to convey the information. Please don’t be insulted if you already know it or know of a better way.
I don't know what type poles you're using, but 6x6 probably. Based on the picture you had attached, right now I would put my headers (2x10 or 2x12) up that will support the trusses. Determine the height of the wall, ie to the bottom of the trusses. Start at one corner post and mark this height with your square and pencil on the OUTSIDE of the post. Drive in a small nail and pull a string from there to the post at the other end. No larger than your barn is, you can use a string level to get close. Have the string pulled TIGHT with your string level near one of the center or interior posts. Then take a step ladder and a four foot level and check the level of the string near the center of the pull. You may have to adjust your level up or down and inch or so where you added the second nail to get your string level with the 4’ level. After the string is level, using your square mark east post with a pencil at the level of the string. Do this around the structure. You may be out of level a fraction, but it won’t show up or be a problem here.
Now you have marked all the posts at the level where the TOP of your header will be. Again, the headers will be on the outside of the posts. Measure down from the line on each post (the width of your header timbers) and make another horizonal mark with your square and pencil. After this is done you can cut the top of the posts off at or just underneath the TOP line.
Now you have cut the tops from all the posts and they are marked where the headers will be placed. Using a skill saw with the depth set at the thickness of your header (probably 1-1/2”) make a cut at the BOTTOM line across the post. Make additional cuts 1/8 to ¼” apart above the first cut until you have scored the post from the bottom line to the top of the post. Using a hammer and chisel, clear out the rough matter left between the saw cuts to leave a relatively smooth face. You should have a notch cut into the outside face of the post that the header can be placed into and be supported by, with a smooth face up the outside of the post. This should be done at each post. Corner posts will be notched on two faces.
Now the posts should be ready for you to set your headers. I recommend using galvanized carriage bolts/nuts/washers to attach the header to the posts, but some people nail them. Keep in mind that the notch cut in the post will bear the weight.
After you have attached your headers to the posts all the way around you’ll want to “eyeball” each wall to be sure it remains a straight line. You may have to push or pull some of the posts into position and brace them well. Once your walls are straight and braced and you’ve check for plumb again at the corners you’re ready to start putting up your trusses.
I believe you indicated that you wanted the trusses on 4’ centers. The trusses on each end should be flush with the outside face of the post and header underneath it. You should measure from one end down each wall header and mark where each truss will fall using a square and pencil. I recommend using hurricane clips on each end of every truss. They are cheap and available at building supply stores. I’ve also found that a using a good cordless drill and deck screws makes it easier to install these clips than hammer and nail, but that’s personal preference.
As far as raising the trusses… Don’t know how much overhang you allowed for at the eaves of the building. I like two feet to keep water away from the building, and it gives you enough “tail” on the truss to make it easier to raise. Two people can raise the trusses, but three is better. NOW IT BECOMES APPARENT WHY YOU PUT THE ROOF ON BEFORE YOU ENCLOSE THE WALLS. Assuming that the trusses have been fabricated and are stacked near the building. Drag your first truss into the building across one end resting upside down on one rafter. With one person on a stepladder at the wall, the other person raises the end of the truss up to him to rest on the header, with the point (peak) pointing at the floor. Then the person on the ground goes to the other end of the truss and lifts it, sliding it back to allow the second end of the truss to go up and over the header. The THIRD person if he is there can help in getting it up and in place. At this point the truss should be hanging upside down between the headers on the outside walls. The person on the floor will need a “pushpole” to push the peak of the truss up to a vertical position. You’ll be surprised how easy it is once you try it, as most of the weight remains on the headers. I’ve generally used a 2x4 with a “V” cut in the end that is long enough to comfortably reach the top of the truss from the floor. With the truss hanging upside down, and a person at each end to stabilize it and keep it from falling too far over or falling back, swing the peak of the truss back and up, insert the push stick to a place where it won’t slip, and slowly push the truss into a vertical position. Once it’s vertical you’ll need to align it carefully, to ensure the overhang is correct and that it’s flush with the face of the posts and header on the outside. You’ll need to brace this one from the ground to keep it plumb and from falling over.
Now you should have your first truss in place and braced. Go back to the pile and get the second truss, drag it into the building upside down and hang it from the headers where you have marked for the truss to be installed, and repeat the “raising” procedure above. To brace this truss, take two pieces of lumber that you’ll be using for lathing, 12’ to 16’ long, Nail one end to a rafter of the first truss about six feet up from the outside wall, letting it extend over the second truss. Do this on each side. Get the second truss plumb and put a nail through the brace into the rafter on each side of it. The length of this bracing extending out will help to stabilize each truss that is raised, as it generally droops a little, and that little weight and friction caused by the braces contacting the truss will help to hole it in place until it is plumbed and nailed to the brace. When you get to the end of the brace simply add another one just above or below the first.
NOTE that when you get near the end of the building you’ll probably have to put two or more trusses up before nailing them in place depending on the pitch of your roof. It’s a pain in the butt to install the trusses and have ONE left on the pile and realize it won’t go up in the space between the last one installed and the header across the end wall. It’s not a problem unless you forget. Just raise them and lean them back against the previously installed trusses. Then install the truss at the end of the building before positioning the last one in it’s place. HOPE THIS IS CLEAR???
Now, all the trusses are up and temporarily braced. They should be checked again for plumb. This may require a little nail pulling and repositioning. After this is done you need to put in three courses of “strong-back” bracing the length of the building over the “joists” of the trusses. The trusses should have a vertical brace at the center, and if the trusses have been installed and aligned properly, all of these braces should be in line. Lay a 2x4 across the top of the joists of the trusses against the center brace. Nail the end to the joist of the truss on the end of the building. Ensure that the truss at the end of the building is straight and the wall is braced if necessary to keep it straight. Then check the next truss for straightness by pulling a string or having someone else “eyeball” across the joists to be sure it’s not waving. Put a couple of nails through the 2x4 strongback into the second truss joist. Continue down the length of the building. This should result with each truss being straight at the center point, and a continuous brace tying all together the length of the building. Install another course of strongback on each side of the truss, about midway between the vertical braces at the center and the outside wall.
After installing the strongbacks, you need to put in some vertical diagonal braces.
A b c d e f g h I
A b c d e f g h I
A b c d e f g h I
A b c d e f g h I
1 2 3 4 5 6 7 8 9
Each column above represents a truss installed plumb within the length of the building. As said earlier, there should be a vertical center brace in each truss, and you should have a strong-back installed at the center at this point. A 2x4 brace should be nailed to the edge of the center brace extending from the peak of truss “A” downward at a 45degree angle to the bottom of truss “d” at point “4”. Each truss should be nailed to the brace between A and d. From the top of truss I downward at a 45 to truss g at point 7. On the other side of the center braces, From the bottom of truss A and point I to the top of truss d and then down to truss g and point 7, etc. THIS IS A GENERAL CONCEPT. Your diagonal bracing should include all trusses and extend the length of the building. This adds substantial strength to the building.
You now have installed your bracing and should be ready to put up the lathing to support the metal roofing. I recommend treated lumber for lathing because of the condensation of the metal. I believe you indicated that you were going to use 2x4’s for this purpose. I noticed some threads mentioning installing the lathing on edge. This is not necessary. Installed flat against the rafter, a 2x4 lathe across a 4’ span will give plenty of strength. In my shop I used treated 1x4 and have had no problem. I generally put the lathing @ 24”oc, but you can use 16” or whatever but I wouldn’t go more than 24. When you put the lathing down there’s really no need to cut it so it joins at a rafter. Just but the next one to the first and continue. Where they but together you can cut a short (10”) block of 2x4 to splice them together. Put the block underneath the but joint and clamp with a c-clamp. Using deck screws put 3 or 4 screws through the ends of each piece of lathing down into the block. That will give the spliced joint enough strength that it won’t move and will support the metal or you walking on it and it makes the job go faster with less waste. Try not to have all of your splices between the same trusses. Start at one end of the building with a course of lathing, and at the other end for the next, etc. HOW MUCH OVERHANG do you want at the gable ends? I usually let it go out about a foot. If you want a foot of overhang, allow your lathing to extend about 15” beyond the end trusses. Measure out from your truss and mark the cut-off point of the top and bottom lathes, trying to insure that you are square to the ridge or top course of lathe. Ensure that the lower marks on either end of the building are the same distance down from the top. Do this on both ends of the building.
Top_a top_b
Bottom_a Bottom_b
Assuming that the distance from top_a bottom_a is the same as from top_b to bottom_b, if it is square then the diagonals from top_a to bottom_b will equal the diagonal measured form bottom_a to top_b. A fraction of an inch on this measure will not be significant. However, keep in mind that the line from top_a to top_b must be in line with the peak of the roof.
After you are satisfied that your lower cutoff marks are square on both ends of the building against a line from top_a to top_b you should use a chalk line and pop a line on each course of lathing and cut it to length with a skill saw.
After cutting all of your lathing to length, you need to install your “show” rafters in each gable end. Again, I’ve found that I prefer a cordless drill and deck screws to a nail in this situation.
At this point you should be ready to start putting the metal roofing on.
Z
X
X
X
X
Y
The diagonal above from Z to Y represents the show rafter at each end of the building. Your lathing is installed on it and the metal will rest on the lathing. You probably want the metal to overhang the woodwork on the eave a couple of inches. On each end of the building take a piece of 1x4 about 3’ long and tack it to the show rafter at the lower end, letting it extend out about a foot beyond your wall. The top edge of the 1x4 should be flush with the top of your lathing. Take the length of your metal sheets and add 1/2” to it. Using that figure, measure from Z down to your 1x4 and make a mark on the top edge of the 1x4. Do this on each end of the building. Drive a small nail at the mark on the 1x4 on each end, and pull a tight string between them. You’re ready to bring up some metal.
Place your first sheet of metal, allowing just enough at the end edge to cover your lathing and try to get it aligned as closely as possible with the string at the bottom. It should be ½” from the string, but parallel with it. Put one screw at the top and bottom to hold that sheet in place. Bring up a second sheet and put it in place. Is it holding the proper alignment with the string? If not you should be able to tell about now much you need to move the sheets and which way. You may have to remove the screw you put in the first sheet’s lower end to make adjustments. After you have the adjustments made if required, put a couple of screws in the second sheet and bring up the third. Readjust if necessary. With 9’ of edge up there you should be able to determine whether the alignment is OK. Get it right and screw these 3 sheets down. From there on it should be a piece of cake.
