A dozen, maybe 15 tops. That’s how many people Los Angeles designer Alan Grant, AIA, expected at a public meeting in Tacoma, Wash., a decade ago. In fact, more than 300 autophiles showed up to view his sketches for the LeMay–America’s Car Museum.

After Grant presented, everyone was silent. “This guy in overalls—probably 60 years old, heavyset, tough looking—raised his hand,” Grant says. “ ‘I don’t know much about architecture,’ the man said, ‘but why can’t it look more like a car? Why can’t you put a bumper and headlights out front?’ ”

Grant, who had his own eponymous practice for a decade before cofounding Large Architecture, thought, “Oh, boy, here we go.” Then he realized that the man had a point. He ditched his boxy design and started over, by not so much mimicking a car but by adding curves and a gleaming finish.

The crowd was even bigger for his next presentation, he says. “The same guy raised his hand and said, ‘That’s more like it.’ ”

A version of that design now rises above Puget Sound like the hood scoop of a vintage Ford Mustang. Inside the 165,000-square-foot museum are 350 vehicles, one-tenth of the Guinness World Records–honored collection of the late Washington refuse-company magnate Harold LeMay. Revamping the design was a bump in the road compared to Grant’s next obstacle: getting the project built on a public–private partnership budget that shrank from a pie-in-the-sky $180 million to a reality-bites $20 million.

Museums, like hospitals and other institutional buildings, tend to be expensive to build. But Grant didn’t want convention to dictate his client’s budget or his vision. Besides, this was a space to exhibit (read: park) cars. “Why can contractors put up a parking garage for $60 or $70 per square foot,” he asked, “but they can’t build a museum for less than $400?”

His solution: an eye-catching silver shell over a parking deck that masquerades as a museum. “Visually, we tried to put emphasis and cost on the roof itself so that the concrete substructure [which includes three dozen 22-by-50-foot tilt-up panels] would not appear front and center,” he says.

To make the budget work, Grant collaborated with Seattle-based engineering firm Magnusson Klemencic Associates (MKA) to design an attractive and efficient roof support structure from glued, laminated timbers, or glulam beams. Engineered by Western Wood Structures and crafted by American Laminators, the 19 massive curved beams, spaced 23 feet o.c., measure 8-3/4 inches wide by 52-1/2 inches deep and arc 104 feet over the exhibit space below.

Unlike the uniformity of a barrel vault, the front and rear of the asymmetrical roof taper slightly, and one side dips below the other. As a result, each of the 757 purlins (5-1/8 inches, spaced 4 feet o.c.) that forms the roof’s secondary support had to be custom cut, and each purlin hanger angled uniquely. Plywood sheeting, 1 1/8 inches thick, covers the purlins; to conform to the 17-foot-radius roof curve, contractors sandwiched flexible 1/2- and 5/8-inch-thick plywood sheets to match the 1-1/8-inch thickness. Next came waterproofing—a self-adhered membrane sheet of rubberized asphalt by the metal roofing–system fabricator Bemo, topped by a waterproof mineral-wool insulation by Roxul.

For the roof finish, Grant looked to London’s Thames Barrier, a rotating floodgate with nine concrete piers clad in standing-seam metal. “It’s beautiful how they glisten in the low evening light,” he says. “Tacoma has similar low sunlight.”

Architectural Metal Works, in Tualatin, Ore., installed the Bemo 400, 18-gauge (.04-inch-thick) aluminum roof. Covering the 79,000-square-foot surface required 67,500 pounds of aluminum coil up to 110 feet long. Roll-forming the panels on site reduced transportation and labor costs. The machine-rolled, locking seams had enough give to suit the variable construction tolerances of the subtly undulating roof. All told, the 10-inch-thick roof system has an approximate R-value of 30, while the 14-inch-thick tilt-up walls come in at about R-21, thanks to batt insulation installed between the concrete and an interior steel-framed stud wall.

Once the foundation was poured, Grant says the structure went up in three or four months. Perhaps, most impressive, was that he delivered a museum for less than $120 per square foot. “We wanted to design something very grand and simple at the same time,” he says. “It was an opportunity to create something with the volume of a train station, where you can see it from a distance and understand the real aesthetic of the automobile.”