Encourage all businesses to roof with solar panels.
Ways of doing this could include government subsidies for new buildings going up if they build the roof/walls exposed to the sun with solar panels. Or, the company could use the energy it generates instead of having to pay for electricity from other sources or receive a reduction in taxes or something if their building provides power for the city's grid. This could also apply to houses, but I say businesses because I was thinking of skyscrapers due to the fact that they are so exposed to the sun most of the time.
I was just at the BCIT green roof research centre yesterday. In a presentation, the Director of the centre showed slides confirming that it is very much possible to have BOTH a green roof and solar on the same roof. The plants benefit from a bit of shading from the solar in the heat of summer, and the PV panels work better when they are a little cooler, which is created by the presence of the plants. They should definitely be involved in this initiative. They have the expertise, and can also educate others about their findings.
Marie C commented
Is there a way to do a mix on a roof of part solar panel and part green roof? Power generation and less power required, combined into one solution. Is it being done anywhere yet?