In the top United States markets, spec homes, meaning the ones built by developers without a specific buyer in mind, have become increasingly popular in recent years, especially at the highest levels of the market.

“If you would have told me five years ago that there would be a Hamptons spec house listed at $40 million, I wouldn’t have believed you,” said Susan Breitenbach, a Corcoran agent who works exclusively in tony communities on the East End of Long Island. “But now there’s one listed at $40 million, and quite a lot in the $16 to $35 million range.”

Located in the Hamptons and also cities including Los Angeles, Miami and Aspen, these spec homes are nothing like the modern boxes or McMansions of days’ past. Instead, they boast over-the-top features, like outdoor movie theaters, indoor basketball courts, turntable garage floors and waterslides that drop from the master bedroom into a pool, plus high-end finishes, like imported stone floors and custom carpentry, that demonstrate the developer’s great attention to detail.

Because spec homes are no longer built to appeal to the largest swath of the market and instead are meant to attract the most discerning buyer, they’ve largely outgrown their previous reputation of being considered tacky or cheap compared to a custom new-build or an updated resale property with lots of character and history, experts say.

“We’re now seeing spec homes that are just as nice as any custom home—if not nicer,” Ms. Breitenbach said.

In addition to being in demand, they can also be a good buy when you factor in their turnkey nature, the often-valuable land that they’re built on, and the new trend toward a high level of detail that keeps the end user in mind, experts say.

When it comes to time, spec builds are meant to be move-in ready, a factor that’s hugely appealing in luxury markets where most people own second (or third or fourth homes). In Aspen, Douglas Elliman broker Rob Bordan said that while there’s always been a healthy spec market, ultra-luxury projects, like one located a half-mile from the gondola and listed for $32 million, are new.

The main appeal of these spec projects, he said, is that a house fit for the highest net worth individual could take two to three years to build from the ground up. “If a buyer’s only going to use the house for a few weeks, or up to four months of the year, most want something they can begin to enjoy more quickly than that,” he said.

In Miami, time and other lifestyle factors have also driven the popularity of high-end spec developments, said Jay Parker, the CEO of Douglas Elliman’s Florida brokerage. “More and more people are looking for turnkey solutions,” he said, adding that they’re also looking to avoid the headaches that come with new construction.

“In a city like Miami or Miami Beach, if you don’t know all the ins and outs and the right people, you could be delayed and compromised,” he said. “A great home can be destroyed by the casualties of new development.”

In the Hamptons, which is also primarily a second-home market, time is also important. But so is the quality of the land, and sometimes, the only way to get the best land is by purchasing a spec home, Ms. Breitenbach said. “Some of these builders bought the land a long time ago,” she said. What’s left either isn’t that great, or has risen exponentially in value, she said.

Brokers in other markets agreed. In Los Angeles, for instance, developers who own prime land in neighborhoods like Holmby Hills, the Bird Streets or Bel Air—often bought during the recession—had the option a few years ago of selling it when things starting picking up or developing a house on the property and then selling it.

The developers that chose to build a spec house and then sell made some serious profits, said Adam Rosenfeld, the founding partner of L.A.-based brokerage, Mercer Vine. A developer who raised a spec house on North Hillcrest Road, for instance, bought the land for about $12 million and likely paid $20 to $25 million to build the house, which was more than 20,000 square feet and like no spec house L.A. had ever seen, Mr. Rosenfeld said. He went on to sell it for $70 million. “People saw that and thought, ‘Wow, what a return,’” he said. “That’s what got this whole crazy trend in Los Angeles going.”

“Since then, we’ve seen a lot,” he continued, “and a lot of them have been really successful.” One spec house even sold for $100 million, Mr. Rosenfeld said.large_2bf3888e-8545-40e4-acf1-6239c80f3cb4

But even with a great piece of land, a spec house also has to be done right to be worth the money, experts say. “People are building specs now with the understanding that they need a team of people to do it right,” Mr. Bordan said. “The designers matter. The interiors and finishes matter. It’s almost like you’re building a spec property with the mindset of someone who has significant wealth.”

In the most expensive spec houses, Ms. Breitenbach noted, a buyer who gets in early enough also has the option to customize. “If you don’t want white marble in the kitchen and want something else, you can do that because you’re dealing with a high-end builder, a high-end architect,” she said. “The whole team is there, so you can fine tune it and make it your plan and your vision.”

Overall, whether a spec home is a good buy can come down to the equation of how much it would cost to buy the land, hire the top team, design and build the property, Ms. Breitenbach said. For a Bridgehampton spec house that her husband is building, which is listed at just under $20 million, Ms. Breitenbach said it would cost about $11 or $12 million to purchase similar land, close to $1 million in architectural fees and $1,000 per square foot to build a 10,000-square foot home. If you do the math, “you couldn’t buy the land and do it all yourself for that kind of money,” she said.

But there are other times the math won’t work out in the buyer’s favor, yet the buy still makes sense. In L.A., for instance, Mr. Rosenfeld said spec house isn’t likely to save you money, because you’ll probably pay a premium for the most competitive properties.

In Aspen, this is also true, Mr. Bordan said. “From a business perspective, if you have the patience to buy the land, design the property and build it from the ground up, you are going to have more equity built into your project,” he said. “More than nine times out of 10, the best deal is going to be to do the project yourself, because you’re going to truly get exactly what you want.”

“But that requires a lot of patience,” he added, “and that’s really part of the equation.”

Courtesy of: Anne Machalinski and Mansion Global