WSJournal. The $100,000 Close.

When Rochelle Maize renovated her 6,110-square-foot Beverly Hills, Calif., home, it wasn't a new kitchen or home theater at the top of her list of must-haves—it was a closet.

'We don't call them closets anymore,' says contractor Gary Drake, who says the preferred term for such spaces is now 'dressing room.'

She hired a designer to create a 400-square-foot master closet with a flat-screen television, a refrigerator for Champagne, white cabinetry with silver-leaf etchings and a large crystal chandelier. Total cost: $100,000. "I wanted to feel like I was walking into a very luxurious Beverly Hills boutique," says the real-estate agent, who adds that the space, designed by Lisa Adams of L.A. Closet Design, was partly inspired by the Chanel store. "The first thing I do when I go home is go upstairs and be in that space."

Once a secondary space designed primarily for storage, the humble closet is taking center stage. The latest in high-end master closets go well beyond the typical walk-in and are created to look more like plush lounges or designer stores. Clothing and handbags in glass display cases are lighted like sculptures; custom-designed couches are arranged near Baccarat crystal bars or dedicated breakfast areas.

Designers and architects say for some clients, the cost of the closet can rival or surpass that of the kitchen, topping $100,000 for large, custom-designed walk-ins with luxurious cabinetry, sound systems and office nooks. Increasingly, developers and home builders aren't only installing windows in closets, they are also configuring home layouts to make sure the closets capture some of the best views and natural light.

California Closets, the North American storage-space franchise, says spending on customized storage systems was up more than 10% in 2012 from 2011. Ginny Snook Scott, the company's vice president of sales and marketing, says the company has seen increased demand for high-end add-ons like wine bars, flat-screen TV displays and dressing rooms in the past year.

A partial view of Jeffrey Colle's Wainscott, N.Y., closet. It includes antique black walnut cabinets and an island covered with a seamless piece of suede fastened by antique nail heads. It measures 400 square feet and cost $120,000.

"We don't call them closets anymore," says Los Angeles-based contractor Gary Drake, who says the preferred term for such spaces among the designers and clients he works with is now "dressing room." A recent remodel he worked on in Los Angeles's Brentwood neighborhood included a 1,600-square-foot master suite—600 square feet of which was for an elaborate dressing room. The $300,000 space had hand-oiled wood finishes, vaulted ceilings and an entertainment center.

"The closet is becoming as large as a living-room or family-room area in some cases," says Martin Mitchell, of San Francisco-area Martin Perri Interiors. He recently designed 1,300-square-foot his-and-hers closets for husband-and-wife clients; the closets have high-gloss lacquer exotic wood cabinetry and solid slab glass doors designed to display clothing, a jewelry vault, lighting controllable via iPad and a wet bar. To accommodate their large clothing collection, a separate wing was added onto the house.

Melanie Charlton, the CEO of Clos-ette, a New York-based company that specializes in high-end closets, says her typical projects range in price from $50,000 to $250,000, but have gone has high as $2.5 million for a three-story closet with an escalator for the wife of a wealthy industrialist in Mississippi. "It's a becoming somewhat of a trophy room," she says. "[Clients] care about having a nice kitchen, too, but that's old hat at this point."

Some designers say the sprawling closets are in part a reaction to the rise of modern, open floor plans, particularly loftlike great rooms that include both kitchens and dens. Having a closet that doubles as a grown-up lounge space offers a private, adult retreat from open family living spaces.

The newest luxury closets are designed to function as rooms in their own right, often with living-room-style seating with couches and ottomans. "We're seeing the closet become more of a social space," says Alison Schwartz of online real-estate tracker Move.com. Ms. Adams, who founded L.A. Closet Design five years ago, says she tells clients to think of closets as multifunctional living spaces. "[Friends] want to hang out there, they want to see what you have," she says. Going through clothes to purge older items can be done "with your girlfriends over wine." Yvonne Colacion, an interior designer based in Los Angeles, designed a massive two-story closet for a client; she says it has become her client's favorite place to sit and read a book.

For men, closets are evolving into something akin to high-tech man caves. Ms. Adams says she's designed closets for men with breakfast bars for yogurt, cereal and drinks and leather couches for watching TV. "It's a living space, more than just for grabbing clothes," she says. Interior and closet designers say glass sneaker displays with lighting from below and sunglass drawers are also popular features.

Showpiece closets are also an answer to a minimalist design aesthetic found in contemporary homes, becoming a practical space to house bulky furniture and other items. "Why would you want to buy some big hulking 6-foot-wide piece of furniture when you can put it all in the closet?" says Diana Augspurger, past president of the Association of Closets & Storage Professionals.

Then there are the options now offered by new technologies that were once only viable in commercial spaces. LED lighting, once cost-prohibitive for home use, generates less heat and eliminates the fire hazard of having lighting very close to clothing. Lighted clothing rods and shoe racks, and automated lights that turn on when cabinet doors open, are popular features. Window coatings that block UV rays also give the option of natural light while minimizing its clothing-fading side effects.

Sinks for makeup application, as well as small refrigerators for delicate cosmetics, are recent requests that Mr. Drake, the contractor, has accommodated. Ms. Charlton of Clos-ette says a new feature she's including in recent designs is a "virtual styling tool" consisting of computer screens and iPads set up in the closet so people can work remotely with a stylist who has a visual inventory of their clothes to scroll through.

Nancy Selldorff, a full-time mother in Boston, is currently in the midst of a yearlong gut renovation of her 12th-floor condominium. She says closet space was a major impetus for the project, which also includes expanding the kitchen into a large great room. When completed, her master closet will become the first space she enters in her 850-square-foot master suite. The space will have Wenge wood cabinets, backlit glass shoe and purse racks and a center island with a white leather top.

"I really wanted a place that felt special and was a personal retreat," says Ms. Seldorff, a client of Ms. Adams. "When I get dressed everyday it makes it feel like a special event."

Condo developers are also taking note of the growing appetite. Echo, a condominium in the Miami-area that recently hit the market, will have some 2,800-square-foot units with 300-square-foot master closets, more than 10% of the total floor plan. The closets, part of 700-square-foot master suites, will include "midnight bars" with coffee machines, wet bars and a small refrigerator; buyers can pick from several chandeliers. Units range in price from $900,000 to $3.1 million.

In Los Angeles, developers of Beverly West, a 22-story condominium with 35 residences, allotted some of the homes' premium space for closets, giving them glass walls with views of the city's skyline and green space surrounding the building. Typical closets in the complex measure around 400 square feet, and were meant to appeal to buyers who might be moving into a condo from a large home, says director of design and development Eric Jencks. Prices range from $1.4 million for smaller one-bedrooms to $22.3 million for a penthouse.

New York-based designer Jennifer Post, who has created homes for celebrity clients like Matt Lauer and Jennifer Lopez, says she has been allotting more square footage for closets lately, typically keeping spaces sleek enough that they'd fit in with the overall look of the home. "You can't tell the difference between a kitchen cabinet and a dressing drawer," she says, with custom millwork and finishes similar to those elsewhere in the house. Hamptons-based designer/builder Jeffrey Collé says his home has a 400-square-foot closet clad in antique black walnut with arched doorways, cathedral ceilings and an adjacent gym and sitting room—features that many clients have since requested.

While some owners erect luxurious closets as a retreat, others can't resist showing them off. A New York building, 250 West St., recently hosted the annual Hearst's Designer Visions showcase, in which fashion designers Badgley Mischka took over a woman's large closet.

Closets have come a long way from their early 19th-century origins, when homes were built with small master closets, typically not much larger than the door leading into them. In the 1950s, sliding-door closets were introduced, according to California Closets, and the walk-in first emerged a decade or so later. Larger walk-ins came into fashion in the 1980s.

Designers say the move toward more elaborate closets first began five to 10 years ago, and accelerated among wealthy homeowners with the debut of the 2008 film version of "Sex and the City," when Sarah Jessica Parker 's character, Carrie Bradshaw, sees a home with a sprawling walk-in closet big enough for her large shoe collection. Mr. Mitchell says the "hers" side of his client's 1,300-square-foot space was inspired by the closet in the film.