We build all our walls out of 2x4's and 1/2" plywood, sometimes double sheeted. This is because our customers like to go through them. If we built it with the 2x2 oe 2x3 and 1/4" luan plans that some people use, our haunt would fall apart in about an hour. We have about 1100 walls built like this and they take up about 7 semi trucks, along with the other 8 full of props. All we are required to do is spray everything down if fire proofing liquid, no special paints or anything, but it all depends on where you are and who is inspecting you. Everyone seems to have to do something diffrent to satisfy their inspector.