you can use almost anything.
the 18x18x24 exo-terras are ok, I have one that houses a female and right now the male is in there with her, too.
I have another female that lives in a custom 29gal slider tank (also has a male in with her right now).
20 talls work well, but a 20 long will work, too, if you turn it on end

the 15
gal hex might work nicely if you can fashion a lid of some sort. otherwise I'd say the exoterra or 20tall would do just fine. as long as they have room to roam and lots of plants, you're all good.