High efficiency appliances and energy efficient cooling and heating systems, tankess hot water heaters, good insulation and choosing the correct orientation and glazing are all excellent ways to improve the energy efficiency of a home. The single most effective way to decrease the energy use of a home is to have a smaller home.

It will need smaller systems and less insulation because there is less of it to insulate, heat and cool. PLEASE remember that oversize equipment uses more not less energy, therby decreasing its efficiency.A smaller homes obviously takes fewer materials to build. Of course, given my bias as a residential resale specialist, I say buy an existing home. They tend to be smaller. You can reuse a lot of the materials or recycle them to others if you plan your remodeling carefully.If you must add space think about converting a garage or using the basement or attic before increasing the footprint of the existing house. Reuse as much as possible, perhaps in a different way. The tongue in groove ceiling could become the floor in an office. Recycle what you can't reuse and buy materials made from recycled materials whenever you can.

I have always been a fn of metal roofs. If you are not going to have a vegetated roof consider metal. Most of it is made or recycled steel and it lasts next to forever--then it gets recycled again!