An important part of any green roof is the filter cloth (it keeps the soil from clogging the roof drains, which can lead to roof failure) . ELT, the maker of the Green Wall technology we showed recently, also makes pre-grown green roofs. They have a "bioblanket" that is both the necessary filter and a root retention system, made of a 50/50 mix of polyester and, you guessed it, hemp. Now if they grew bamboo on the roof we would have the perfect TreeHugger product. ::Elevated Landscape Technologies
Read more on Green Roofs in TreeHugger here.