A 10 gallon would be fine when it's young, but taller than the standard fish tank is more ideal. One of those 18x18x24 exo-terras would be good for an adult or two, a larger tank wouldn't be wrong though. Getting usable perches near the top of the tank is also important. Care sheet:

Frog Forum - Gray Tree Frog Care and Breeding

Quote Originally Posted by Bombina Bob View Post
I know grey tree frogs have very similar care to green tree frogs Hyla cinera
and the forum had a grey tree frog caresheet but i cant seem to find it :/
Glad I'm not the only one. I think it was bumped off the 'Care Article' page and I can't see how to get to page 2 or if there is a page 2...I find it by googling 'grey treefrog caresheet' and it's usually near the top. Sad I know, but it works.