the outer part of a home
Metal Roofs absorb less heat and reduce the need to cool a home by 20-70%. Metal is also an excellent surface from which to capture rainwater. Since long roofs last a long time it "eliminates the need for landfill disposal of old roofing" (www.classicmetalroofingsystems.com/about-metal-roofing/environmental-benefits/).
Vinyl siding is made of recycled material which helps the environment. "Vinyl is an inexpensive siding option with excellent built in insulation properties" (http://www.calfinder.com/library/siding/types-of-siding/recycled).
Solar panels use the light from the sun's rays to generate energy. Over time solar panels save money and make your houses value go up. "Solar power production generates electricity with a limited impact on the environment as compared to other forms of electricity production" (http://www.engineering.com/SustainableEngineering/RenewableEnergyEngineering/SolarEnergyEngineering/WhySolarEnergy/tabid/3893/Default.aspx).