well, you really dont need a lot of room for these frogs for their first 5 years of life, they wont be any bigger than an orage, a small 5 gallon should be good enough, especially because, as said many times, they just dont move.
I have the one frog in a ten gallon tank, fully equipped with partial aquatic area, a nice cool side/warm side, yadda yadda, he doesnt care, never moves until the food starts coming around, and even then, not too much, so as long as their environment is moist and warm, i doubt they need anything deluxe