Grey TFs are one species I've never kept but always wanted to.

The way you asked the question it's a bit hard to give advise because you don't mention the size of your tank, so it's difficult to say. IMHO you can create the viv the way you want to; meaning put whatever size water feature that you'd prefer, just make sure the frog has alot of sturdy branches and leaves to climb on because it's nocturnal and arboreal.