Abstract: Extensive green roofs help improve urban environment. To explore the feasible ways to promote roof greening in highly urbanized areas in China, this paper has summarized the course of green roof construction in advanced foreign countries and the difficulties in extensive green roof construction on existing buildings. It has takes Shanghai, a forerunner of roof greening in China, as an example and carried out suitability assessment of roof greening on existing buildings in the city’s central urban area (districts within the Outer Ring Road in Shanghai, with a total area of about 667.80km2). Most of the foreign countries advanced in green roof construction have gone through the development pattern from encouragement to coercion and from new buildings to existing ones. Construction of extensive green roofs on existing buildings is more challenging technically. Structural innovation, substrate optimization, plant selection and cost control are required. Shanghai has taken the lead in issuing mandatory policies on roof greening. Related techniques have been developed, but there are still limitations in construction types. The construction of extensive green roof has great potential in the city.