I'm all for helping friends with small jobs around their house, but have learned that when money exchange takes place the dynamic of the relationship changes.
There's always the 'well I expected this that and the other for the price' and then what do you do?
Not only that, you're taking money for a job at considerable height...personally I'd rent a Genie or some kind of lift to reach the space as I hate ladders, and they're the #1 killers on a job site (IIRC from my Working at Heights training).
I don't know enough about the actual work required (and plenty here have good ideas) just be sure it's worth it. A small Genie / lift is about $300-500/day. Rent it for Saturday and you can get Friday/Saturday/Sunday for the price of a single day sometimes if the guy behind the counter is cool with it.
Good luck, and be safe as ladders are dangerous.