The New American Home, a demonstration project in Las Vegas, rambles a bit at 8,800 square feet, but it boasts a number of energy-saving features. In this rear view of the four-level home, solar panels can be seen in the foreground. The showcase house was unveiled last month by the National Assn. of Home Builders, and although a buyer has requested that its price be kept secret, the home is reported to have cost $4 million.