Re Roof Pitch etc;
Easiest of all, Yellow pages, roof trusses, give them the dimensions.
They do all the calculations etc, snow loads, storage or home (different specs).
For 32" you'd need 17 trusses and 1 x 3 furring strips to brace her up.
Fabricated trusses are always made from nice dry wood so that a 20' + OH is easily handeled and installed with a 3 man crew.
You walk them in and lift one end in place (upside down) and then the other side.
Once they are all up there you flip them over one by one and toe nail into place with 1 x 3's to brace things.
2 men do the nailing and the 3'rd guy flips them from below with a long 1 x 3 that has a 4" nail at the end to hook the top for pushing/flipping.
If decking with ply/aspenite be sure to respect 24" centers.
Basically a 20 x 32 ft trussing job is a mornings work.
For the first truss, you want to nail a temporary ,say, 2 x 4 vertically on the blbg end with it sticking up higher than the truss.
That's so that that first truss wont rotate over the side of the building.
All told the factories can supply trusses for about the same price as you will pay for the lumber and that's not counting your labor. (except if your helpers cost $1.00 hr and you work for free)
They have no wastage but you end up with all sorts of 6 to 20" leftovers.
Plus they install all those plates with hydraulics.
To build without trusses you'd need to use 2 x 8 rafters (or 2x6+cross ties) and poles and you'd still have sagging as the loads would want to 'spread' the walls.
PLUS them 2x6's or 2x8' will cost more than trusses!
Been there, done that!
For me it's a no brainer. Prefab trusses!
Since you are doing the install, you can optimise spacing of the 1 x 3 braces to best use that attic space for storage area.
If you slide in plywood sheets (before decking the roof) you can obtain lots of useful storage area.