I think most of the advice here is spot on. I don't agree with treating this topic with the same regard as straight males trying to court straight females. A certain wooing standard is expected for heteros and homos looking for a relationship, sure. But here we have a guy who is trying to explore a sexual interest, before delving into the lovey-dovey courting methods.
What I mean is, the OP is curious as to whether or not he would enjoy sexual interaction with another dude. This is something to explore and determine before getting into a relationship with someone of the same sex. So, I don't think it is offensive at all for a straight guy to approach a gay guy regarding the sex. Some of us gay dudes have known we are as queer as a $3 bill since the get go, but I'd venture to say that most of us have had to be curious first to find out. In this way, I feel that his roomate (or any gay guy) would be able to empathize with the OPs curiosity and not be offended at a proposition to explore the OPs sexual interests.
Now, you can go about it in a whole slew of ways. I would suggest tact and an overall expression that you need help figuring this out, and you really want the roomate to help you - but, OP, do you have the hots for your roomate or is he just the closest openly gay guy around? It's true many gay guys want to do the naughty with their straight roomates, but it is less offensive to the gay guy if the "straight" guy has an interest and is not using the gay guy as a cum dump. Granted, some people are into being cum dumps, but many aren't and to assume that really makes you an ass.
Basically, there are ways you can approach this without being offensive, and there are ways that will get you nominated for biggest ass of the year. Displaying your sexual confusion, desire to explore, and a respectful interest in your roomate being the one to try it all out (like saying how you are most comfortable with him, you trust him more than anyone to help you through this, etc) is a good start to winning him over and getting some gay action. Like others have said, remember it is a give and take kind if thing. Unless he is into it, don't treat him like he's the fag for sucking your cock. Be humble, remember HE is doing something for YOU, and be grateful..maybe even offer to service him. Keeping things open and honest and as close to both party's desires as possible (ie you respecting and understanding his limits, and him yours) is key to making something like this work out so no one gets hurt.
Last thing I can say, is if he does agree and you do go through with it, be caring and respectful. Make sure he is really ok with it, reiterate to him how you don't want to use him, how thankful you are he is willing to help you, etc...that attitude is what builds a relationship up and also will let him decide how far he wants to go with you (oral, anal, role-play, actual relationship, etc...)
Lastly, good luck and have fun. Giving and receiving bjs is fun IMO!

