Here's some things you want to look for:
Top floor, corner unit.
Vent to the attic in closet or wherever you want to grow.
Make sure no necessary equipment maintanence people might need to get to is in the closet, i.e. air conditioning units, electrical wiring, etc.
Big closets (obvious reasons).
Make sure there is electrical outlets near the closet, or even better, in the closet, which is rare.
Just be aware that it is almost a certainty that someone you dont want in the unit will have to go in there, whether it be maintanence or exterminators, whatever. I have a six month lease and its happened 3 times to me already.