To the real estate editor: Regarding a recent question in which one of your readers indicated wanting a prefab square house with an atrium, I believe she could find it by writing to Timberpeg Homes, 24 Low Road, Hanover, NH 03755. The company will ship the precut materials for a house of your own design. In other words, Timberpeg architects will complete the home to your custom specifications. They are quality homes -- the best prefabs. C. J. Wilkins Highland Beach, Fla.