Dark Rapture, I would not call the laws here that strict. For just smoking it all they could do in my state is give you a citation, $10-20. In my actual city they would most likely just tell you to put it out, drop it and leave should you be in public. In your own house they can not even do that. The only odors they can enter your house over would be like dead somethings, gas leaks and the odors of a meth lab.
You can actually pay taxes to the state here for illegal drugs. Should you get arrested they can not charge you with tax evasion and this is where some of the stiffest penalties come from. They are usually more leinant on drug dealers who comply with this law as well.
As for the actual problem at hand I would not worry about it. If you roommate is smoking that much that the smoke itself is entering the room maybe it is time for an intervention of some sort. Otherwise I would think it is probably just the odor that is entering. Weed is a very pungent flower. When it blooms it stinks sometimes up to miles away. If you are smoking in your house then your air system is probably already circulating some of the harmful elements all around your house anyway. Not smoking in your room is about the best way to minimualize harmful effects given your situation of an in house smoking enviroment.
I myself just go outside to smoke. My closest neighbors are a couple of horses, a bunch of cows and two of the most bizzare donkeys in the world. None of them are going to tell on me, though.