are u talking about background scenery to put behind glass or some texture background to put inside a tank?
i just have stick-on jungle backgrounds for my 2 tanks. like these:
but some peeps have 3-D textured backgrounds also. u could buy them or back them. i've canned insulation foam used before. use that as a base and carve/shave it or stick it with rocks, bark, bones, plants, etc. etc. u know spray foam like this:
i hope to pickup some Uroplatus gecko's during our fall Reptile show and i'll be putting them in a bioactive vivarium. i'll probably be using spray foam to create a background they can climb on.