Right now I have two setups going on - I have my 3 girls in a 20 gallon tank with 2 stories of topper (it's over 3 feet tall total, and has full floors), and then Curly is in a 10 gallon tank until I get a different cage (he's still pretty small though).
I've been looking at different methods of making cages, and really like the whole cube stuff idea, so I might give that a go. Are the holes too big for rats though?
Also - in your setups, do you have a "litterbox" or do you have Carefresh (or the equilivent) in the whole bottom?
i don't think night is attacking anyone at all. she is right, tanks are terrible for rats. and cages to fit three rats in aren't that expensive if you know where to look, i got mine for $45 (although i'm planning on upgrading).