The hard part is having a shorter tank is that makes it a bit less friendly for tree frogs. Though with 27 inches tall, it isn't impossible. My reds are in a 24x18x24, but they tend to go vertical rather than using horizontal space. Personally? I'd do a large group of darts (a breed that can be kept in groups.) Research which dart you would enjoy the most and build them an awesome huge paludarium. I believe a chameleon needs a taller enclosure and heavily ventilated ?full screen cage? as well as high humidity (that means keeping ambient humidity up.)