As a billionaire developer, Donald Trump built casinos, luxe condo towers and lush golf courses. Now, as president, Trump aims to develop perhaps his most ambitious and surely his most contentious project yet: A wall along the nearly 2,000-mile U.S.-Mexico border.

How? At what cost? And who would benefit?

Much remains unknown. Ultimately, though, experts say the project, if built, could deliver a windfall for some large construction companies and their suppliers. Engineering and infrastructure companies that have worked on previous government projects could capture a chunk of the multibillion-dollar work. Among them are Kiewit and Flour Enterprises. Subsidiaries of both have signed up as interested vendors.

But the project would likely also be stymied by the struggles that have beset the industry in recent years, notably a shortage of skilled labor and rising materials costs.

Here’s what’s known and not known about the potential effects on U.S. construction companies and workers:

———

Q: Which companies would likely work on the wall?

A: The government has laid out plans to hire contractors for design and construction. Some smaller businesses would serve as subcontractors. One factor the government is to consider in choosing contractors is their track record in hiring small businesses as subcontractors and making significant use of them. The Customs and Border Protection agency has set a goal of having 38 percent of subcontracts go to small businesses.

Roughly 850 companies have expressed interest online in being vendors. Among them are self-described small, disadvantaged firms, like Nationwide Construction Services of Jacksonville, Florida, and Northwest Geotechnical Consultants of Wilsonville, Oregon. Some of the big companies include a subsidiary of the construction and engineering firm Parsons Corp. and Vulcan Materials Co., a producer of asphalt and ready-mixed concrete.

“It probably will take a really big general contractor that is used to managing multiple projects under one large umbrella and that will need many suppliers,” said Ty Gable of the National Precast Concrete Association. “It’s going to help a lot of individual suppliers along the way.”

The Trump administration has said it wants the wall to provide not only a physical barrier but also access roads, motorized vehicle gates, lighting, communication towers, ground sensors and remote video surveillance. That would mean job opportunities for companies beyond construction firms. Some that have expressed interest include Border Technology Inc. of Hereford, Arizona, whose website says it’s worked with the Border Patrol using drones and other equipment to monitor the border.

———

Q: What kinds of jobs are we talking about?

A: Along with engineering and design work, the project would require numerous construction and heavy machinery operators. Among the jobs: Truck drivers to ferry materials, crane operators, concrete workers, digging-equipment operators, site supervisors and general laborers. Any employees who work on-site would have to pass an immigration and criminal-history check.

Finding enough skilled laborers could be tough, though, because thousands of skilled construction workers left the industry after the housing meltdown and Great Recession a decade ago.

“It ultimately comes down to how much they’re willing to pay,” Ken Simonson, chief economist for the Associated General Contractors of America, said of the contractors. “Firms would price in the difficulty of recruiting workers in their bids for doing the work.”

———

Q: How long might it take to build?

A: Unclear. For now, the government’s contract solicitations are intended only to assess prototype designs for the wall and to build some segments of the structure. In addition, acquiring land from private owners that would be needed to build the wall would likely add delays.

———

Q: What might the wall look like?

A: The government has been inviting companies to submit designs for a wall made of either concrete or other materials. The idea is to evaluate several prototypes before deciding on a design and material.

The wall is envisioned being as high as 30 feet, with automated gates for pedestrians and vehicles. The wall would also extend at least 6 feet underground to deter tunneling across the border; be resistant to climbing tools; and be strong enough to withstand attempts to make a 12-inch diameter breach in the wall using a sledgehammer, drill or other power tools.

And, among other things, the Trump administration wants the side of the wall facing the United States to be “aesthetically pleasing in color.”

———

Q: What benefits might the wall deliver for the U.S. construction industry?

A: Given the estimated cost — somewhere between $8 billion and roughly $20 billion — the project would represent just a thin slice of overall U.S. construction spending. Spending last year on public construction totaled $286 billion. And that was just a quarter of overall construction spending, which includes residential and commercial developments.

Still, “as a single project, it would dwarf everything else,” Simonson said. “Even if it came in at the low end, a single $8 billion construction project would top anything else that’s out there now.”

———

Q: How soon will a design be chosen?

A: Companies have until Wednesday to submit prototype designs. Up to 20 finalists will be selected to make more detailed design renderings and an oral presentation in Washington. The government would then award a contract based on sample walls that are to be built in San Diego. Initial documents laying out the timeline for how companies should submit wall designs indicated that the government wants to finalize a design and begin awarding contracts as early as May.

———

Q: How much would the project cost?

A: Unclear. Trump has suggested that the project would cost $12 billion. Congressional Republicans have estimated it could go as high as $15 billion.

An internal report prepared for Homeland Security Secretary John Kelly projected the cost of building a wall along the entire U.S.-Mexico border at about $21 billion, according to a U.S. official who is involved in border issues. The official spoke on condition of anonymity because the report has not been made public. An estimate by engineers at the National Precast Concrete Association puts the cost of the wall at $8 billion. This would be for a design made up of reinforced concrete panels, with some portion of the panels extending underground. Not included is the potential cost of acquiring land.

“That’s the variable that probably gets these numbers much higher than $8 billion,” Gable said.

———

Q: Where would the money come from?

A: The White House’s budget proposal to Congress included a $2.6 billion to forge ahead with the border wall.

Critics — Democrats and some Republicans — have argued that a border-long wall is unnecessary and have chafed at the notion that Trump wants to draw upon U.S. taxpayer money, even though he promised repeatedly during the campaign that Mexico would be forced to pay for the wall.

It’s unclear how soon Congress might act on Trump’s request or how much money might be approved or appropriated. The government has cautioned would-be contractors that the project is subject to “availability of appropriated funds.”

———

Q: Any other potential hurdles?

A: The Trump administration appears to be bracing for a fight with private landowners over the government’s likely use of eminent domain. Under eminent domain, the government can, under some circumstances, order landowners to accept buyouts for their property to make way for the fence. The administration’s recently proposed budget includes money to hire 20 lawyers to work on land acquisition.

(AP)