Big houses deserve big decks, or at least that's what some luxury homes are getting. Take, for example, the 6,000-square-foot deck attached to the Lake Michigan home of Gaylen Byker, a retired natural-gas executive. It has an outdoor kitchen, a resistance-swimming pool, a spa, a fireplace, and lounge areas. Guests arrive on an electric cart traversing a 1/4-mile-long bridge. Byker isn't alone. Architects are seeing rising interest among luxury homebuyers in backyard decks, even in cold-weather markets. Scott Morris, the sales director for a California developer, put it this way: "If you don't add that outdoor playground, you're just getting it wrong."