With the rapid urbanization spreading across China, more and more buildings are constructed, as a result, the building density keeps increasing and the usable area for urban greening is decreasing. Ideally, there needs to be a certain amount of greening area to ensure the quality of ecological environment in the city. However, because the urbanization process is speeding up and the population in cities is exploding, more and more ecological and environmental problems appear. It is of vital important to improve the quality of ecological environment with limited usable space [1]. According to the investigation from the international organization on ecology and environment, the average per-capita greening area needs to be above 60 m2 for a city to have an ideal environment. However, with large population and high building density in the big cities of China, it is very difficult to hit this target. Base on the studies from the statistical data of China City Statistical Yearbook published in recent years (Fig. 1 and Fig. 2), the average urban per-capita greening area in China has been increasing since 2000, however it is still well below the recommendation limit of 60 m2. Since the building roof is considered as the 5th cubic plane, roof greening has become a potential opportunity to increase the greening area and improve the quality of the ecological environment