There are LOADS of good places at Butler to study. People often figure out what works best for them and stick with that most of the time. The library is air conditioned, and I really like studying there when I need to buckle down and get stuff done. When I'm just doing my day to day studying, I usually just stuck to my dorm (and now my apartment). The dorm usually doesn't get loud enough to be a problem. The noise level will depend on the people in your hall, though. I always found that putting headphones on a listening to music would allow me to block any distractions out. Between classes, I've become a fan of studying in the lounge in the basement of the pharmacy building. There are actually two libraries on campus - the Science Library and Irwin Library. A lot of people also like going into classrooms in Jordan Hall over the weekends to study. There are study rooms in the dorms - ResCo has two in each hall and there are some in the Schwitzer basement.
As for roommates, there is a whole form you fill out before coming freshman year, and I bet that you could request to be paired with another prepharm major. A lot of the time, prepharm majors get put together anyways, probably because their study habits are a lot alike!