When Tia Sinclair-Bell decided to buy a backyard playset for her 7-year-old son, Khalis, she wasn’t inspired by what she found at local showrooms. Everything was just too basic and boring, and nothing seemed like much fun. So the New Jersey mother and band manager, who is married to musician Ronald Bell of the disco-era band Kool and the Gang, turned to the Internet, and discovered that she could work with builder Barbara Butler to design her own playhouse.

Ms. Sinclair-Bell originally planned on a $12,000 playhouse to complement her 9,500-square-foot Millstone, N.J., home. But as the planning process went on and Khalis got involved, the fort became more and more ornate. The final design included a tube slide, a rock-climbing wall surrounding the entire structure, escape hatches, a stainless steel fire pole, rope ladder, a bridge with swings and monkey bars, and water cannons “to keep marauding pirates away,” Ms. Sinclair-Bell said. The result is a jaw dropping, multicolored, 15-foot-high fortress, christened “Club Khalis,” with a price tag of $46,730. Ms. Sinclair-Bell calls the four-month project an investment.

At suburban residences and country houses, parents are thinking outside the box, literally, and custom-ordering what could be defined as playground paradise. As more builders start cashing in on this newfound childhood indulgence, the variations are becoming increasingly elaborate.

FAO Schwarz, the Fifth Avenue luxe toy retailer that emerged last Thanksgiving from bankruptcy, now sells two versions of these high-end, outdoor play structures, where the amenities offered read like a list of new construction options for homeowners. The toy store’s La Petite Maison is designed in the style of a charming Victorian and features such options as indoor plumbing, electricity, a grand staircase, a media room, and a heating and air-conditioning system. The 8-foot high ceilings, recessed lighting, bay windows, and dry walled interiors come standard with the $30,000 price tag. For those looking for something a bit less pricey, FAO’s tree house, the Monkey Mansion, is a mere $12,000, and comes with its own tree.

It’s hard to pinpoint who first conceived the idea of these children’s minimansions, but Ms. Butler, a California-based builder whose backyard designs are found on estates throughout New York, New Jersey, and Connecticut, says the first time she heard of an interest in lavish playhouses was in 1987, when Bobby “Don’t Worry, Be Happy” McFerrin called her office. Ms. Butler admitted that she wasn’t Mr. McFerrin’s first choice – he called her after several other companies turned down his request to customize a backyard playhouse.

Ms. Butler, who has a background in designing outdoor furniture for grown-ups, jumped at the opportunity to create something different. She soon fine-tuned her skills to exclusively design backyard play structures. Today, some 18 years later, her client list is filled with moneyed parents and grandparents. Sprinkled among the Wall Streeters and dot-com successes are Robert Redford, Kevin Kline and Phoebe Cates, and Will Smith. Grateful Dead guitarist Bob Weir worked with Ms. Butler to design an outdoor children’s theater, complete with tasseled velvet curtains and a full backstage. (And yes, Ms Butler said, she’s certain that the rocker has even jammed on it himself.)

Real estate agents say the playhouses can be a sound real estate investment. “I’ve seen some backyard playgrounds that are equal to or nicer than some houses,” said Michael Daly, vice president of the Corcoran Group, who manages 13 offices on Long Island’s East End. “Clearly, it adds value to a sale.” Mr. Daly said that lately there’s a significant increase in the numbers of grandparents looking to buy houses that are along the lines of family compounds. “They’re often seeking properties that have wings to the main residence so grandchildren can have their own area. These outdoor play structures are becoming very important to the sale.”

While the trend toward adding more indoor luxuries to playhouses continues, even Ms. Butler has limits. “I like the idea of a structure being more rough and tumble,” she said from her office in San Francisco. “Some of these custom designs are more fussy than I normally like. It’s not about being carpeted and closed off. It’s about physical and imaginative play.”

Even city dwellers admit to a touch of envy. “Sure, these things are impressive,” said one Manhattan mother of two, whose flooring company has carpeted more than a few of these suburban playhouses. “But my kids will have to make do with community playgrounds.”