Do you recall the Hanging Garden by King Nebucchadnezzar? Even during that time, having plants not just on the ground has been thought of. Now, especially in urban places, it is even encouraged to have plants living atop the roof especially for greening to help the environment.
There are two ways to do this: by having a green roof or by having a garden roof. What is the difference? The garden roof is primarily used for design like atop a condominium where residents can go to, to relax or enjoy the view. At the same time, having those plants help oxygenate the environment, although not as concentrated as the green roof where much planning is put into especially the roofing and the irrigation system. While the former serves two purposes at low degrees, the latter serves one, the environment, at a high degree.
In terms of insurance, I believe green roof has a higher value since the amount you spend for the roof is higher too. Same goes with rv insurance, it the roof has a solar panel, more likely than not, the insurance coverage is higher too.