What would be a fair deal to build a web site for friend?

I'm a second year CS student. I've got a bit of coding experience and very little web development experience, but I've been wanting to learn more and build an actual site.

My long time friend and roommate / landlord has an idea for a website. Sounds like a pretty good idea to me. It's not a simple website. It would most probably involve a database. He's been trying to get me to work on his idea for maybe a year or two now. I've got plenty of ideas of my own to work on, so it never seemed like a good idea to work on his idea instead of mine.

Now the situation has changed a bit and he wants to pay me now to work on his idea. I need / want a part time job and I've been procrastinating on working on my project, so it's starting to sound like a good idea.

I'm to figure what a fair deal would be with him. I'm basically going to be coding the whole site and then maintaining / upgrading it. He'll be paying me to work on it and then if there's profit we would split that, say 50/50. Obviously I can't charge what a web design firm can charge since I still have a lot to learn and it will take me way longer than it would take them. His first idea was just to pay me when I'm done, as a half finish web site wouldn't be that useful to him. I was thinking he could just take off a certain dollar per hour rate off my rent for how many hours I work on it. Say if he paid me a token rate of $10 / hour (since I'll be doing a lot of learning). Or hybrid of the two might also work. Say $5 / per hour every month off the rent plus another $5 / hour when the site is complete or a milestone reached.

I really have no idea how many hours it will take me to complete the site or what a fair price would be, if he was going to pay in a flat rate or what a fair $/hour would be. Any thoughts on what would be fair price or payment structure?