It's fine in the winter, when the roof becomes a giant solar heat collector. But there's no way to turn that giant solar heat collector off when the hot weather comes around.
A study has shown that if the 100 biggest cities painted all their roofs white, and switched their road materials to lighter colours (ie concrete instead of asphalt) it would reflect enough light and heat back into space to entirely offset the global warming of the last few decades.
It's not a proper fix for the problem, obviously, for that, we need clean, sustainable energy. But it could buy us enough time to make the changes we really need. I feel myself going all green all of a sudden.
"He who wonders discovers that this in itself is wonder". M.C. Escher.