The helicopter completed its task of shuttling materials and hoisting beams into place in the course of just one day. Here it is about to set down a cargo-net-load of plywood on the landing area nearby the house. Most of the materials needed to build this 2,800-square-foot house, situated 1/4 mile off the coast of Connecticut, were brought to the island by helicopter. The logistics of using a helicopter to build a 2,800-square-foot house on a three-quarter-acre patch of land in the middle of Long Island Sound gives new meaning to the phrase "nerve wracking." But to contractor Ralph Indorf, president of Indorf Construction Company, Inc., of Yorktown Heights, N.Y., it was exciting, even