The problem with a tegu in that size enclosure is height. Not that they climb all that much as adults, but because they like to DIG. You will need at least 18" of dirt, preferably 2', and that, well, uses up the whole enclosure. If you can only provide 2 feet of height then I would recommend a ground dwelling snake, such as a Blood. Retics need height as they are semi-arboreal, and that size isn't adequate for an adult of 15 feet plus...
Chris