Wow. "Jerk" doesn't even scrape the surface where this guy is concerned. Before you pay him anything, know as much as you can about him. Suppliers, competitors, BBB, contrators' licensing bureau, etc. would be a way to start.

The fact that he has no signed work order/agreement would leave him wading in his own doo-doo in court, so no need to worry about that.

He even sounds like the kind of guy who would come back and tear his work apart just for spite!

What I would do is this: Have the work inspected! I would send him a bill via registered mail for the inspection to be sure it's up to code and done right. If it needs correction or additional repair, I'd also send him that bill.

I would further send him a non-threatening letter indicating that you are perfectly willing to go to court over the situation should he elect to take that course.

If he persists, I would seriously look into ordinances against trespassing and the like. This guy is giving roofers a bad name.