If you're going to be heading in to any kind of adversarial situation involving contracts, then you're probably already outmatched; your roommate will go to his dad, and then whether you've drawn up your own contract or purchased one or consulted with an attorney of your own, you'll still be staring down the barrel of a lawyer whose son is involved. Lawyers love nothing more than billable hours, except presumably your roommate will getting a pretty healthy chunk of them for free.

So, I don't think you can make this work out.

But, if you wanted to try anyway, I'd suggest drawing up your own contract as a counter-offer. They aren't hard to write, and they don't have to be long. They just have to describe, in very plain language, what work you'll perform, what you expect to receive in return, and what to do if things don't work out.