Well, as long as your material does not absorb water, it should be good. Plastic is best, but for those of us who either don't have access to it, or can't afford it - melamine or some sort of laminated wood products works best. Otherwise - you have to coat it in either polyurethane (which takes forever to dry and cure out) or line it with heavy duty contact paper.
As for the doors: if you are using plexi - use the thickest material you can find and make sure you put plenty of slide bolts on the doors. The rule of thumb is: if you can bend it - so can your boa. If you are a pretty good carpenter, it would be best to make a picture frame for the plexi doors, so you don't have worry about the snake escape artist in your collection. Regular glass doesn't bend, so the thickness required is based on how large the piece of glass will need to be.
Good luck with your cage building!