The other reptiles are in store-bought tanks, one 100-gal, and two 50ish-gal. It's an interesting idea to build the new cages over the other ones, but that adds permanency to the location of the iguana tank. My hope is that I can build it in such a way that it can be taken apart and reassembled when I move out of my parent's house. The dimensions are 6' tall X 4' deep X 6' long. That should be plenty big for the next year or so, and the way I have it planned, I should be able to just add on extra length or height as needed.