The bottom line is that you should be able to save some money with this project at the cost of a little work if the metal sheeting and trusses are OK. If so, be sure you mark each metal panel, maybe on the inside with a permament marker, in such a way that you know where it came from. When you rebuild, be sure you put your lathing down in such a way that you can put screws in the old holes. The vinyl or whatever washers under the screw heads will seal just as well on used metal as new if you're using the same screw or nail holes. Even if you have to replace the poles, the trusses and lathing should be good. You may not can use everything, but everything that you can use will save you some money. BE SURE TO SPACE YOUR LATHING ON EACH FACE TO MATCH THE SCREWHOLES IN THE METAL THAT YOU REMOVED to eliminate leaks, or trying to patch holes. Good luck from this point. You're already lucky to have this opportunity I think.