If your snakes are housed in a room with warm ambient temps (~82), and a good relative humidity, I would recommend an open air rack. I've built a couple modifying these exotics by nature's plans, and I love them. They are very functional, and very lightweight. I know Tim (Muddoc) has built some like these too, and has been pleased with them. I still have some melamine and plastic racks, but I plan on switching everything over to open air in the future. If your tubs need to be warmer than room temp though, you'll probably need a closed rack design. If using wood, you'll want to use 3/4" for structural integrity, but be warned that a rack built with any wood product will weigh A LOT! Let us know what type of rack (open/closed, adult/juvie, size etc.) and those who have built a good number of racks could give you better advice.

-Evan