....I guess I have more questions than suggestions here ... like "have the 2 of you ever included others in your sexual activities before?" ... "have you ever fantasy played having a 3rd person involved with the 2 of you? ... "is this primarily YOUR desire or has she ever mentioned involving others?" ... "is this roommate black as to the reason you're mentioning it in this forum?" ... and do you know what HER sexual fantasies are?
Starting out a relationship which involves others can work ... I'm an example of that. My college roommate dated my wife for 2 years before breaking up with her to date another girl. So my wife and I had 2 years to get to know each other on a friendship basis, she came to me for a shoulder to cry on, and it developed from there. Our first time involving others in our own relationship was with a girl who was her initial roommate in college ... we did a 'couple swap' a few times with them ... then a few 3-somes with guys. When we married 3 years later we just decided to continue occasionally involving others. We decided to stop a few years ago when our ******* got too old to work around them.
Any relationship is only as solid as the open communication you establish with each other ... if either of you have problems with being able to talk things out, it indicates a weakness in the relationship. As Torp mentioned, setting boundaries & parameters to this kind of activity is very important ... involving others in your sexual activities should be to recharge your energies for each other, not distract from your relationship with each other. Also, I'd use caution in involving a "roommate" as the closeness of this individual could lead to their own sexual activities when you're not present, leading to emotional involvement that could destroy the relationship the 2 of you have.
Good luck with it if you do it ... Mac