what size are you looking for? where in the world is this building. is it modern, or ancient? depending on alot of what your doing, i found using styrene to build to be the cheapest. but i know your young and may not have alot of knowledge (hence your asking...i know im a brain sometimes
). if your using 1:35 scale figures...1/4 thk wood can be used as well. perhpas other's will have more ideas for you!