The minimum size enclosure for an adult Savannah Monitor is 4x4x8. Obviously this would be a custom built enclosure. A do-it-yourself gig if you could. I can't wait until my Sav (Dino) is that big. Oh wait yes I can. He has time yet he is still under two feet long. Fatty boy though. Good luck with your project.
the cage needs to be as long as twice the monitors length, as wide as the monitors length and needs to be tall enough to allow for a layer of dirt thats atleast half the monitors length.