Thats the smallest you can go, but if you put a 4 foot Argentine in there and don't take it out for atleast 2 hours a day, its gonna get bored, and try to escape. Alot of the time Reptiles will rub their nose on the edges of the cage, it can injure their nose, in extreme cases, the reptile can actually erode their entire face off till there is bone, teeth and guns exposed. If you can't devote alot of your time to keeping your Tegu happy and occupied, then an 8x4 foot, or for more efficent space, a 7x5 foot. Another thing to remember thats a good rule, the cage should be atleast twice the length of the full grown animal. But if you intend to buy a Baby, I have mine in a 60 Gallon tank till she gets older. Hope this helps.