You give the green roofs initiative too little credit for the damage it will cause, The impact will be far less great on downtown, and much worse elsewhere. You ignored that it isn't only new buildings, but all buildings over 25,000 square feet in floor area (a two-story commercial building with a 12,500 square-foot footprint will have to comply, for example). Outside of downtown there are far more existing buildings that will have to retrofit green roofs when they do roof replacements. Many are one-story older commercial structures in areas that don't attract the revenue stream from higher rents that will allow owners to afford the retrofit. This is a coming wave of decline.