A little hint for the Left:  If you want to try to persuade people to do what you want them to do, you might be able to convince some people to go the "green roof" route.  But when you want to make it law that mandates it, and you're going to enforce at the point of a gun, you're going to run into a lot more opposition.  

If it's good idea, why does it have to have force and coercion behind it?  Why don't you just let people do it they want to, and if they don't want to, nobody's going to force it on 'em.  That's the way it was done when we were a free country in the olden days.