Basically, a green roof is a sort of rooftop garden. To create a green roof, you lay down a waterproof barrier, material for drainage, a layer of soil, and plants [source: Greenroofs.com]. It's best to have a contractor experienced with eco-friendly designs help plan and build a green roof, since the weight of the plants and soil might require that you increase the supports for your roof. An expert can also help you pick low- maintenance plants that will thrive on your roof. The plants help insulate, filter rainwater, and combat habitat depletion for some area wildlife [source: Pelletier].
Green roofs can be as simple as a couple of types of ground cover or include a beautiful mix of moss, succulents, ground cover, and even herbs and plants. The complexity really depends on your budget and how much maintenance you can manage. There are two types of green roof: extensive or intensive. An extensive green roof, which is more low-maintenance and uses less soil, can range in price from $8 to $25 per square foot to install, while a higher maintenance intensive green roof runs $25 to $50 per square foot, requires more soil depth and can support a wider variety of plants and even trees [source: Pelletier]. Because intensive green roofs cost more and require a less sloping surface, they're more common on commercial buildings.