Hmm.. It sounds like a good idea but rather than buying a pre-built cabinet you'd probably save money if you found plans for a cabinet (or snake enclosure) online and then buy the materials from Home Depot or Lowes. It would probably be cheaper to get the materials this way and they can cut the boards to size for you.
I'm not sure if you could slide tanks out safely without anchoring the whole structure to the wall..?
I'm sure some of the other DIYers will chime in here when they're on and be much more helpful than me.