Picture of green roof

Quick answer：

A green roof is a roof that is covered with vegetation and a growing medium, which provides insulation, improves air quality, and supports biodiversity. Green roofs can be found in various forms, from extensive systems with a shallow layer of growing medium to intensive systems with deeper soil and plants similar to those found in a traditional garden. They are increasingly being used in urban environments to mitigate the urban heat island effect and provide other environmental benefits.