I am very worried about environmental quality so I am concerned when I see things that might sound nice but tend to support the idea that environmentalists are impractical idealists. I would support building standards that increase efficiency whether through insulation and windows, solar panels, innovative HVOC, or green roofs.
Data from the green roof at the botanic gardens indicate water might be necessary.  If roof loading is limited by having only 4 inches of soil many things will not do as well as plants that have access to deeper moisture.  Transpiration is an important part of cooling and xeriscape has a relatively low value.
I have an area with trees, grass, flowers, and shrubs that I water every week or two, another area I never water, and a garden or orchard area. I can feel the difference in heat between the areas. Data also show that green roofs retain heat at night in the summer which may increase evening cooling loads.
I need comparison data to make an informed decision.