St. Louis • When Mike and Steve Roberts began building Roberts Tower in 2007, the downtown loft and condo market was already showing signs that leaner days were ahead.

The Robertses — brothers and business partners in hotels, broadcast towers and other real estate projects — remained confident as they pursued their $70 million luxury condo building. But a year later, those sluggish signs transformed into a national housing crisis, claiming St. Louis' biggest builder of downtown lofts and condos, Pyramid Construction.

And yet, the Roberts brothers press on with construction of their 25-story condo tower at 411 North Eighth Street — the first new residential high-rise since the Mansion House complex went up in the 1960s.

"They're trying to tap probably the most difficult market now for the downtown buyer because they're trying to tap the high-end luxury market," said Chris Grus, a real estate agent who operates mostly downtown.

It remains unclear when the building will be competed and when the Robertses will start selling. The brothers have been tight-lipped on the project's progress for months.

In December 2008, Steve Roberts said the first Roberts Tower residents would move in by early 2010. But in January, construction appeared to have slowed to a crawl as winter winds whipped through the building's windowless upper floors, leading to speculation that the Roberts brothers may not be able to finish the project.

In March, they sought a city building permit for $2.75 million in work on the lower floors, expected to feature a restaurant and meeting space connected to the adjoining Mayfair Hotel, which the brothers also own.

Meanwhile, work at the tower has accelerated in recent weeks, and a "coming soon" banner hangs from the tower's south side.

Grus is among those who say a Roberts Tower condo will need to fetch at least $350 per square foot to turn a profit for the developers. In the current slow market, the highest price paid in the past year for a downtown condo was $220 per square foot, while many lofts in converted downtown warehouses cost less than $150, Grus noted.

The Roberts brothers said last year that they plan to compete the exterior and build out the 55 planned condos as they are sold. The brothers are promoting "green" construction with high-efficiency windows, high-end appliances and floors of sustainable bamboo. They also are promising perks such as private catering, car washing, personal shopping, handyman services and dog walking.

"Long term, when the economy fully turns, they should be good to go," said Bryan Keller, head of RubinBrown's real estate services group in St. Louis. "Long term, that is a beautiful project."

But what happens in the short term is the critical question. The tower can succeed if it survives what will remain a tough market through at least the end of 2010, experts say. Grus wonders whether it might be best to wait for the housing market to rebound before selling units — if the project's lenders would agree to such a delay.

"By 2012, downtown will support luxury housing," he said. "There's now a grocery; there's Citygarden."

While high-end condos can be found elsewhere in the region, such as in Ladue, Frontenac and Town and Country, the Roberts Tower won't face a direct downtown competitor for luxury condos. The only comparable property is the Edison Condominiums, built a decade ago in a former shoe warehouse at 400 South 14th Street, said Kevin Farrell, director of economic and housing development at the Partnership for Downtown St. Louis.

Farrell says a misconception exists that downtown has a glut of unsold condos. To cope with the lending crisis, developers in the last two years switched hundreds of condos to rental apartments, drastically shrinking the for-sale market.

"The positive of that turmoil is that it has provided some very good units on the market that were planned as condos and were switched to apartments," Farrell said. "They've filled up quickly."

The Roberts Tower wasn't the only new luxury condo building planned for downtown before the housing crisis. Skyhouse, a 22-story luxury condo tower to be built at Washington Avenue and 14th Street, was in the works until plans collapsed in 2008.

Skyhouse partners had presold about 30 of 166 planned condos, but by the summer of 2007, the number of deposits dropped from several a month to zero, Riley said. A lot with parking and patchy grass is all that remains at the site.

Ben Riley, president of RileyWaldrop and a partner in the Skyhouse project, said he had urged his Chicago partner to delay Skyhouse until 2012, when downtown would more likely have the stores and services luxury condo dwellers demand. He said he doubts today's downtown can support a luxury high-rise.

In fact, Riley said, the market might require the Roberts brothers to reduce condo prices so much that the tower turns out to be a money loser.

"Or to take the optimistic approach, they might have a lot of rich friends who will buy all the units," Riley said. "They've definitely put millions and millions of dollars into the building. Obviously, there's no turning back."