It really depends on the growth of the animal.
A typical male Veiled that is about 16-18 inches long would need something like LPR08 suggested.
That is a bare minimum though.
Would you want to live in a single wide trailer?
I think I would prefer something like a 3 bedroom 2 bath.
If I were you I would shoot for a 24x24x48 or if you are tight on room you can go smaller.
I have most of my chams in 20x20x50-52 custom made cages.
I think it is a good medium, becuase of the added height.
My juvenille female veiled, she almost 5 months, is in this size cage now.