Construction of the $1.1 billion Minnesota Vikings stadium is shifting in the next couple of months toward an innovative roof, installation of five pivoting glass doors and the placement of 66,000 seats that will ring the field.

With 1,200 workers on the site daily representing more than 300 Minnesota businesses, Dave Mansell, Mortenson Construction's general superintendent of the project, said Monday, "We've got a critical couple of months. We're transitioning."

All of the concrete has been poured. Only three more large pieces of steel need to be picked up in the center bowl of the project, Mansell said. In two weeks, the biggest crane on the project will be broken down and moved off site the same way it came on — via 70 truckloads.

The stadium, roughly half of which is taxpayer funded, is 65 percent complete and set to open in just over a year, in time for the Vikings to kick off the 2016 season in their new home. About $1.5 million worth of work goes into the project daily.

On the site, it's a whirl of activity and heavy machinery — the airwaves filled with constant beeping from all directions, the warning signal of the backward movement of heavy machinery.

For one more season, the Vikings will play on the University of Minnesota's field, then they move to the glassy facility that team Executive Vice President Lester Bagley said will be the "best in the NFL."

Faithful fans appear ready for the new digs — the Vikings say they have sold 40,000 of the 49,000 stadium-builder seat licenses they have put on the market. To purchase a season ticket in the new stadium, fans must buy a license for most of the seats. The proceeds go to the owners, Mark and Zygi Wilf.

Signs hoisted

Visible signs of the building's progress emerged on the outside even during the hourlong media tour Monday. The U.S. Bank sign was hoisted into place on the eastern zinc wall, a silvery logo set against a shiny black wall that will soften into a gray patina over time.

U.S. Bank has paid the Wilfs an undisclosed amount for the right to place its name on the wall for two decades. To celebrate the occasion, U.S. Bank and the Vikings catered a lunch of Jucy Lucy cheeseburgers for all the workers Monday and provided each with a purple hard hat stamped with the Vikings horns — similar to players' helmets.

Mortenson executives shepherded more than 20 journalists through the site, providing as much detail as anyone could want, including the provenance of the zinc in the wall surface — Rodez in the south of France, according to Mortenson's Eric Grenz, who went to visit the site.

Senior project manager Brendan Moore pointed skyward to a construction worker walking across netting where the roof will be. The worker is part of the crew installing a layer of the glasslike ETFE polymer that will cover the field. ETFE is the more common name of ethylene tetrafluoroethylene, a self-cleaning fluorine-based plastic with a high resistance to corrosion. Because of its tolerance for stress, ETFE is used to cover wiring in airplanes and spacecraft.

Mansell said the roof will be in place by late fall so workers won't be as exposed to cold and snow as they were last winter. "We're right on schedule," Mansell said as he led journalists through the building at his brisk pace. "And you know I would tell you if we weren't."

Glass windows along the concourse on the northern side of the building already provide an unimpeded view of the Guthrie Theater and the Mississippi riverfront.

On the western side, Mansell showed how in the next month, the steel frame of the tallest pivoting door will go in place, followed by the glass. The five doors opening to the plaza are a signature design element on the facility. The doors will hang behind a giant video screen facing the field.

Standing below the screen frame, Mansell showed how the new field will be 18 inches higher than in the old stadium and is being laid on Metrodome concrete.

The new stadium will be almost twice the size of the Metrodome, opened in 1982 and demolished in early 2014. For comparison, Mansell said, the Metrodome's footprint could be laid onto the ground-level bowl of the new stadium and wouldn't even touch the side seating.

As for that seating, the steeply raked concrete base is visible all around the building. Workers were installing rails to frame the seating.

Once the seats start to go in, Mansell said, one will be set into place every two minutes until they are all there next April.

Rochelle Olson • 612-673-1747

Twitter: @rochelleolson