Hi there, @macroy. I work for Sungevity, so clearly I'm biased when I tell you that we're amazing to partner with :-) If you want a more objective view of our customer satisfaction I encourage you to check us out on Yelp:
Sungevity - Jack London Square - Oakland, CA
Regarding your re-roof question, you just need to have a roof that will last the length of the lease. If you're interested in replacing your roof you could re-roof just where the panels are, but sometimes it's more cost effective to do the whole roof. It all depends on situation.
If you decide you want to move forward with panels on your home we would send a professional out for a home visit to confirm your iQuote system and then address any roof concerns.
Happy to answer any other questions you have!