My zoo med terrarium is a 12 x 12 x 12 and seems quite nice for my young grey tree frog. but he is a small species of tree frog, i believe he will only get a to a max of 2 inches long and i wont put more than one in that small of terrarium.
Look at pictures in my album.
Also I am very new at this but i understand grey tree frogs are a good starter frog.
Read the care sheet on them to the left
hope this helped a lil.