ok, so heres the thing. i have a 20gal tank that the girls are currently living in. to me its going to be too small for them as they grow so i got to thinking, they have those "Add a level" things you can put on a 10gal tank, what if i took two of them, ziptie (or whatever) them together and snipped the part that would go over the side of what would be the 10gal to incorporate two fo them (are you following me or did i loose you yet) to get the most out of my 20gal tank.

http://www.petco.com/product/10806/S...e.aspx#details
as an example.. could it work do you think? or would i be better off

a: just buy a 10 gal and the girls loose all that floor space but gain height
b: forget it and fork the money and get something more accomidating like a ferret cage (or martin? cage.. no local retailers i hate waiting lol)
c: buy a large parrot cage and get basically the same thing (less floor space, added height)
d: leave them alone its enough space (not sure it is though as i would like to get one or two more rats eventually)