H-Haus a prefab company based in Sante Fe New Mexico, has a wonderful green add on package to its prefab models. Single or two-story confiuguration with double height entry, wrap around balconies and skylights are standard features in the H-Haus range. For around 10K each, you can add a Rain Water Catchment system, Waste Water Recycling or Solar Panel and Storage Package. The homes are available internationally with model sizes ranging from 600 to 3,000 square feet. The small footprints reduce land use and the homes are constructed with materials that will reduce energy bills and conserve natural resources. The smart, energy efficient design includes super-insulated walls and roofing meeting European housing standards. Link.