[Christ]

Another form of solar energy (You just might LOL)

• Lay rubber on your roof.
• Build up your roof's edges approx 3".
• Drill water vents about every 3" (1" pipe leading into whatever you have for a gutter system).
• Add top soil.
• Plant grass and other small greenery.
• Care for it as normal, except mowing, obviously.

Chemical reactions in the soil create heat (only a little bit), which insulates the house better against heat loss in the winter.

The soil is constantly somewhat wet, making it perfect to insulate against heat soak from the sun in the summer.

Plants naturally dine on CO2, so the more of them we have (or the less we displace, however you choose to see it) the better!

EDIT - This, of course, assumes that you're not going to cover your roof in PV cells.