Vegetative flat roof create buildings and developments that heal rather than harm the environment. They can help by producing clean water and air, reducing the 'hot island effect', as well be a part of healthy community ecosystem.
Traditional flat roof gardens, which need more soil to grow large plant lawns, are labour-intensive, need irrigation, feeding and maintenance. Extensive green roofs are designed to be virtually self-sustaining. Depending on your location there are exciting government grants available for these types of projects!