Is this in the dorms, or off-campus?

Why not be honest with him and just work out some agreement. I mean you should both respect each other equally so if he's going to be studying a lot and wants the room quiet and distraction free all the time, then thats selfish. On the same line, if you want to smoke daily and openly in your room which will get all up in his face, that's selfish of you too.

So why not respect each other and be honest. Work out a compromise. Try to smoke when he's not there (try to learn his schedule somewhat, so you know you shouldn't have to worry about him coming in and having the room all smokey and shit). And on the same lines, he should try to study a good amount at the library (your college should have one, and even if by some weird freak reason they don't, there should be somewhere quiet on campus where he can go). He should try to get his studying done the same way, learn your schedule and know what windows of time he can be left undisturbed.

Learn to compromise, you'll both be much happier and keep your friendship and respect for each other.

And TRUST ME, if you're not smoking, the smell of mj smoke DOES piss you off (cig smoke too, btw). I think if you can smoke in your room when he's not around and properly air it out so it doesn't smell at all (and try not to smoke in your room a lot, because when you're a smoker you don't notice the subtle smell, but a little can linger and be much more noticeable to a non-smoker), then you should be fine. If you can, smoke elsewhere most of the time. You should respect the time he likes to get work done, so if you know he likes to do it, say, right after class, plan not to smoke then. He should also spend some time out of the room. If you lock yourself in and complain about shit all the time, you're hogging the room which is meant to be shared.

Well good luck.