I think it's jaw-droppingly awesome when you see the rare building with green plants growing on it. I'm not talking like some old house overrun with weeds or something, but when plants have somehow been integrated into the actual design or aesthetic of the building, whether on the roof, inside, around, or on the walls of it. Aside from any of the reasons people might come up with for why it's good for the environment yatta yatta, it just looks really awesome. Cities NEED more green, so why not use the spaces we got to grow more green stuff? Buildings can be like templates for new and weird urban foliage, a shift away from all the typical hard grays, blacks, and whites of the concrete jungle.