Excellent presentation. How do you deal with roof loads?

I wish we had green roofs in Los Angeles. We have huge amounts of flat roofs. There are loads of shallow-root native plants that have evolved here to thrive in the climate and which would be hugely beneficial to wildlife. We have high cooling costs in summer and terrible air quality that green roofs would help counteract. I'm not sure what the hold-up is -- ignorance? Most people in Southern California have never seen a green roof. I also brought it up at a talk about the loss of green cover resulting from people here replacing small homes with McMansions and someone yelled at me that we can't have green roofs because we have wildfires here. I'm not sure what one has to do with the other. It's not as though Southern California lawns are regularly bursting into flame -- so why would sedum on top of a roof? Someone else complained about the water shortage. But why would native plants require more water than our fallow, green lawns or swimming pools?