some very good quality ones come from PVC plastic. That's what is used on mine that I bought from HerpEnclosures.com

If you're looking to build, there are a few that use melamine wood from Lowes or Home Depot...it's cheap and it's white, so it's appealing. Someone was supposed to post a DIY, but they never did.

there's a few links floating around for DIY's but i don't remember them..someone plz post them