Where are you located ?

If your roof is well built you could easily make it a green roof. buy some firestone 45 mill EDPM and glue it to the Plywood or OSB (with most of our OSB going to Iraq its about the same price as plywood in most places, so if you are building build with plywood which outgasses less and requires less glue and is stronger and longer lasting and lighter and more water resistant) Also you could look into wood heating with Rocket stove, and solar hot water, and in warm areas planting Fast growing vines on the south side of your house, grapes are nice, so are hops. Also, if you have some land planting some black locust would be a good way to heat your house. Black locust grows quickly and is a dense wood that produces alot of heat.

If you don't have double paned windows they are a great investment for energy savings and retail value. After you do the roof, of course!

Jan