1. go with your homosexual roommate.
2. laugh, talk with your homosexual roommate
3. talk to girl with homosexual roommate / ask her opinion on something
4. introduce yourselves
5. next time, go without homosexual roommate.
6. small talk: how's your week been/ etc. etc.
7. is she receptive / comfortable during small talk? if yes, continue. if no, ABORT.
8. up small talk into "flirtations". ask about personal interests / school. go slowly. look for openings that might suggest she'd be up for hanging out outside the laundromat.