Yeah man, I think you’re gonna want to tell your roommate. Get to know them a bit before you two actually live together (if there’s time), but maybe broach the subject beforehand–it’s important enough to share given that a girl is expecting to live with another girl, not a guy (it’d be the same if you were mtf with a male roommate). I wouldn’t’ve minded if my roommate last year was mtf or ftm transgender, but I know some of my friends who would’ve been uncomfortable (tbh I’m only thinking of two of my friends who’re strictly Jewish Orthodox).
I saw from your post history you go to Bridgewater State University, and here’s something you might want to check out: http://www.bridgew.edu/student-life/residence-life-housing/residential-learning-communities
I’m fairly certain the Social Justice living community will be welcoming to your situation for the years to come, and you’ll definitely find mostly LGTB-friendly people there.
Something I personally think would reveal you as a ftm transgender is the communal bathrooms (if the bathrooms at your school are communal). On the guys side of the hall (and girls on the girls’ side did this too), we would walk to and from the bathroom in towels (sans clothes). In the bathroom getting into and out of the showers, we definitely were in towels. I’d imagine people might notice if you used the male restroom (given you haven’t been taking testosterone), but that’s just something you might want to consider.
Overall, I don’t think you’ll get any flack for being transgender. I’m a strong conservative and a member of the College Republicans at my university, and I don’t think a single person in the club would mind if someone they knew was transgender–college campuses are EXTREMELY progressive. Everyone knows someone who’s LGBT.