German artist Katharina Fritsch's artwork "Hahn/Cock" is unveiled at Trafalgar Square's Fourth Plinth in London in July 2013. The artwork will appear this summer at the National Gallery of Art in Washington. (ANDY RAIN/European Pressphoto Agency via National Gallery of Art)

A giant blue rooster will land on the new roof terrace of the National Gallery of Art’s East Building in July, an early and irreverent signal of the transformation of the museum’s modern art galleries.

Katharina Fritsch’s “Hahn/Cock” will take its place on the terrace overlooking Pennsylvania Avenue months ahead of the building’s Sept. 30 reopening. The 14½ -foot sculpture will anchor a new outdoor sculpture garden, one of three additional spaces created during the three-year renovation of the I.M. Pei-designed building.

“Hahn/Cock” was originally commissioned for the City of London’s contemporary art series in Trafalgar Square. It held court there for 18 months starting in 2013, and in 2014 was acquired by the Glenstone Museum in Potomac, Md. It is on long-term loan from the Glenstone to the National Gallery.

The blue bird will be the first outward sign of the dramatic renovation of the East Building, located across Fourth Street on the Mall. The building will feature two new interior galleries linked by the roof terrace and sculpture garden, creating 12,250 square feet of space. The northwest Tower Gallery will showcase works by Alexander Calder, while the northeast gallery will feature abstract expressionist works, including a changing selection of Mark Rothko paintings.

The added space gives Harry Cooper, curator and head of modern art, flexibility to reinvent the way the museum presents its collections and to incorporate more of the works acquired from the Corcoran Gallery of Art in the two years since its court-approved breakup. “A nice coincidence” is how Cooper describes the timing.

Even before Fritsch’s eye-catching sculpture is installed on the terrace, museum officials will begin moving hundreds of works into the building. Susan Wertheim, chief architect and deputy administrator for capital projects, likens the multi-year process to choreography, with each department performing it duties — from mechanical systems and reinforced floors to gallery configurations — the building has been painstakingly updated.

Everyone — curators, designers, painters, carpenters, electricians, conservators, installers — is working toward one simple goal.

“You try to make the work of art, whatever it is, look the best it possibly can,” senior curator and chief of design Mark Leithauser said.

Leithauser, Cooper and Wertheim offered an exclusive peek into the work that has been going on for more than three years. Gathered in the museum’s design studio, they shared stories of the complex undertaking. Cooper described it as the biggest of his career. “Pure curatorial pleasure,” he said. “This is a dream.”

The curators began with small printouts of works being considered for each show. Paper or foam models are the next stage – think paper dolls, flimsy and flat – and finally, the works still in play become refined three-dimensional models. These are arranged in a dollhouselike model of the gallery that showcase Pei’s quirky angles.

These models are critical to anticipating how the works will relate to each other.

“Art is physical,” Cooper said, explaining the model’s value. “The models are tactile, allowing us to play with space. Of all the toys, the computer programs and virtual reality, the best are the foam core models.”

While Cooper considered which works to include, Wertheim was addressing mechanical and safety systems. Leithauser and his staff are focused on the arrangement of the art, the color of the walls and the lighting. Some galleries are easier than others, he says. “Calder is so difficult because things move around,” he said of the artist’s mobiles. “It’s a lot easier to change things with foam core board than later when carpenters are involved.”

The building will open with three temporary exhibitions, too. “In the Tower: Barbara Kruger” will hang in the southwest Tower Gallery; “Photography Reinvented: The Collection of Robert E. Meyerhoff and Rheda Becker” features a pledged gift of 30 works, and “Los Angeles to New York: The Dwan Gallery, 1959-1971,” traces the career of gallerist Virginia Dwan.

The renovation is a public-private partnership, with donors contributing $30 million to build the new public spaces and the federal government contributing $39 million for the facility improvements. Among the donors are trustee emerita Victoria P. Sant and her husband and trustee, Roger W. Sant; trustee Mitchell Rales and his wife, Emily; and trustee David M. Rubenstein.

To celebrate the reopening, the National Gallery is launching a community weekend Nov. 5-6, featuring live music and performances and interactive tours of the exhibitions. Oct. 13 marks the debut of “After Hours in the East Building,” a mix of music, film and live performances from 6 to 9 p.m. on the second Thursday of the month from October through April.

There’s much to be done in the next five months. Discussions of re-framing some works continues, and after the artwork is hung comes silk-screening text onto the walls, focusing lights, and much more.

And there must be time for last-minute changes, Leithauser said. “You can’t always anticipate the power of one palette, the strength of one piece over another,” he said. “If you can get 90 percent there, you’re in good shape.”