Dear John Stone,
I am writing to you due to my need for a roommate. I believe that you have an empty spot in your apartment and I hope we can arrange a deal. Your place is relatively close to my campus and I see the rental rate is reasonable. You should pick me because I can maintain myself, I can clean and cook by myself and leave things generally spotless; therefore there is no need for you to worry about me leaving a mess. Also, I think we both have the interests so a friendship between us can really strengthen this deal.
Anyways, hopefully you can accept me as a roommate, it's a great choice and it's the right choice.
Yours truly,
[NAME]