Apartment Guru: The Mooch Upstairs

Dear Apartment Guru,

I am a homeowner who intended to rent out the top floor of my home. I did a lot of work myself but was unable to finish the place up. Five months ago a friend of mine who is a skilled carpenter contacted me looking for an affordable place to live. We made a deal that he would work on the place for three months and then move in and pay one hundred dollars less than I would otherwise ask for in rent over the first three years. Well, the guy never "got around" to fixing the place up (I think he came by once or twice and stared at the walls). But because he hadn't made other plans he decided to move in anyway. He paid the agreed upon price the first month, but has since decided that the place doesn't meet his comfort and he doesn't want to pay the amount we decided upon.

I really need the rent, especially now that my own financial circumstances have changed. But the place definitely needs a lot of work. I told the guy (who I am thinking is less and less my friend these days) that he should take up his woes with the "contractor" but I'm not sure what rights I have here. Can you help me out?

-Blaming the Contractor