Roof gardens are enjoying a revival. Landscape architects are now being followed by architects, project developers and owners of roof terraces in discovering the advantages of plants on the roof. In each of these locations, designers took up the challenge of the building, the urban environment above the roof-line or the landscape. Each spot is so different that it had to look for a new definition of the roof garden or roof terrace. They have come up with new architectural concepts using water, stone, wood, metal, glass, trees, plants and grass, created new green spaces or achieved astonishing effects up on the roof.