Stock-house-plan services are everywhere, it seems. You see stock plans collected in books, sold on newsstands, and promoted in magazines where dozens of services offer mail-order selections. As of 1973, there were only about 25 plan companies, but today there are so many, we've lost count. In Atlanta, Ga., alone, where in 1973 there was one service, there are now 13. Though it has become big business, with about 30 large-scale companies offering nationwide service (some shipping as many as 13,000 sets of plans a year) the concept of stock plans is nothing new. Before stock plans existed, builders worked with plans found in "pattern books." The first American pattern book, The Country Builder's Assistant, was published in 1797 by