The size of the feeder wire is determined entirely by the size of the breaker feeding it - and not the size of the breakers, or wires, being fed. As long as those wires come from a 20 amp (or smaller) breaker, they're fine.

To answer your original question, though .... "inside" is inside. If it's got a roof over it, NEMA-1 is just fine. Or, perhaps more accurately ... NEMA-1 is just fine for any dry, or damp, location.