It does depend on how much run or time out of the cage he gets. If he gets out of the cage a lot, it doesn't need to be as big as if he is in there all the time.
I would still make it as big as possible. At least 2*4 grids. 3*3 or 3*4 would give more room. As it going to be a temporary cage, I would just zip tie a pen about 10-12 long and 2 high. That way you can move it around and use a wall (unless he is a chewer) and make it as big as possible. It would be able to be folded when not in use and it fairly easy to pack up and move.