Best way to stop a snorer, elbow him/her in the ribs....hard. Also recommend Breathe Right strips to said roommate, should help alleviate snoring.
The elbow trick works well, when friends and I would get together to play cards and smoke cigars, we had one friend who would snore like a freight train. I couldn't sleep with all the noise so I'd go into the room where he was and literally elbow him in the ribs, naturally he'd get startled and I'd say dude you were snoring. He'd play it all cool and would snore soon after, after 2-3 elbows to the ribs, he'd stop.