Have you thought about checking out metal roofs?Metal roofs are getting much closer in price to asphalt.
- They are green because the metal is post-consumer recycled material and it will be recycled again when it comes off the roof 50 to 100 years from now. I believe the amount of recycled content for metal is a minimum of 85%.
- A metal roof will outlast asphalt at least 3:1. A metal roof installed properly will last 50 to 100 years as compared to about 15 to 25 for a good asphalt roof. So while you might not be thinking that long-term, the longevity of the roof makes it greener too.
I haven't researched the heat island effects of light-colored metal versus asphalt, so I cannot comment on that. I would assume that a light-colored metal would be better than asphalt, but you would need to research the issue.
Metal outperforms asphalt in so many ways. It won't easily blow off the roof in a windstorm, it holds up to hail much better, snow won't stick as easily, etc., etc.
Good luck with your roof!
For more information:
Read David Edwards's Q&A "I'm reroofing a typical sloped roof -- what materials should I be considering?"
Also, read Anthony Addesso'sQ&A "Are metal roofs more energy efficient for southern climates than shingles?"