Wall construction thoughts.....

Does this sound like it makes sense?? I'm planning on making my wall out of 5/8" A/B ply with 1x3" firring strips as studs with styrofoam insulation between the studs. For the interior i'm thinking about 1/8" birch ply. As for the roof, Im planning on using 2 layers of 1/8" ply with the same studs, insulation and interior panels. Do you guys think this will be sturdy enough? Also, I dont want to go with aluminum, I'd like to make the exterior light grey. Should I just use exterior paint? epoxy?
So many questions......where to start!?!?!
jolly
So many questions......where to start!?!?!

jolly