A Green Roof for Your Home

"A green roof is actually a cover for your current roof that uses plants such as grasses and lichens to cover the top of your house. It is actually very in-depth when it comes to making your roof green and the process usually involves water proofing your existent roof, applying a root repellent system and a drainage system so there is little to no damage caused by the plants."

http://freshome.com/2009/01/22/what-are-the-benefits-of-a-green-roof-for-your-home/