If you click here you'll see a Google view of Downtown Greensboro. Other than City Center Park and a few other pockets it is mostly devoid of green or anything that might be green if it were the right time of year. And yet there are hundreds of acres of available space just waiting to be made green... on top of the many downtown buildings there.
If I were in charge of a city that wants to call itself green I would be looking into ways to put more life on the roofs of those buildings. No, not every building as not all are strong enough and most are privately owned but if I were in charge I'd be finding out which City owned buildings could support green roofs and start making them green. Why? Because "Green roofs serve several purposes for buildings, such as absorbing rainwater, providing insulation, creating a habitat for wildlife, and helping to lower urban air temperatures and mitigate the heat island effect.".
And because city government should lead the way. I might even go so far as to reduce property tax rates on homes and buildings with environmentally green roofs.