Green treefrogs do not require a lot of space and actually seem to enjoy sitting in one spot for lengthy periods of time. They can be housed quite comfortably in an all-glass terrarium of at least 10 gallons. In the bottom of the terrarium, create a substrate by placing some plain paper towels. Then, place a small water dish with a length of PVC pipe angled into it. This pipe will serve as a means of escape if your frog happens to fall into the water. Once you have these basics in place, you can add a variety of artificial plants to give the terrarium a more natural look.
To clean the tank, you will simply need to change the substrate, and give the terrarium, water dish, PVC pipe, and plants a bath in hot, soapy water. After washing them, rinse and dry thoroughly and place them back in the tank atop a fresh layer of substrate.
For more information, read Quick & Easy Green Treefrog Care (T.F.H. Publications, Inc.).