A rendering of the new Milwaukee Bucks arena shows the planned design for entrances at the east side of the building and the abstract roof, which begins on northern edge of the building and will be clad in zinc panels treated to achieve a gritty, brown-rust patina. Credit: Populous

The first detailed glimpse of the new downtown Milwaukee arena reveals a giant building with a dramatically arcing roof, curving body, tall sheets of glass, social spaces — and a few challenges yet to overcome.

The Milwaukee Bucks will share the development plans with the City of Milwaukee on Thursday; several renderings were released in advance to the Journal Sentinel. They are considerably more detailed than the conceptual renderings released in April 2015 and represent the first step in a public design approval process that's required for construction to begin.

More importantly, they underscore the broader vision for the signature project, which has been both controversial and more anticipated than any downtown project since the Milwaukee Art Museum addition designed by Santiago Calatrava.

"I think in 10 or 20 years from now, you'll look back and say this was the spark that changed downtown Milwaukee," said Brad Clark of Populous, one of the lead architects on the job. The architects are careful to describe the submitted plans as in-progress.

The shape of the 714,000-square-foot arena's arcing roof has changed subtly from initial plans. The abstract, wavelike form begins near the base of the building on W. Juneau Ave. and arcs dramatically over the glassy entrance.

The roof is the "big move," the statement of the $500 million building, said Clark. It will be clad in long, thin zinc panels chemically treated to achieve a gritty, brown-rust patina. The matte panels can take on a leather-like look and will change appearance in varying types of light, said Gabe Braselton, one of the lead project managers at Populous.

The idea for the wavelike shape surfaced in sketching sessions among Populous architects before the firm had been hired and when the Bucks were still eyeing the Journal Sentinel site, near the Milwaukee River.

"We think there's beauty to the region and water is a big part of that," Clark said, adding that they also wanted to emphasize Milwaukee's industrial grit. "We know that's important to your community."

The new plans reveal a more obviously curved facade on W. Juneau Ave. The sculptural, zinc-shingled side is punctuated with thin windows of varying widths that are angled for a faceted appearance.

"You are going to see these glass slots that go up six stories, that curve over your head," said Greg Uhen of Eppstein Uhen Architects, a local firm working on the project, adding that the north face of the building will be especially striking at night.

The windows will be treated with a ceramic silk-screen pattern to accentuate the curvy shape of the building. The glass will be more transparent where the exterior bulges and more opaque near the base and roof.

The ceramic treatment — called fritting — will be used in varying degrees of opaqueness on horizontal bars of glass on the glassy entrance, which remains similar to designs revealed last year.

The exterior facades facing 6th St. and Highland Ave., which will be opened up to traffic according to the plan, are also being seen for the first time. The 6th St. side of the building, featuring a 30-foot-tall section that is distinct from the main arena structure, features a smaller entrance, a functioning mechanical yard and an enclosed loading dock.

It is the part of the building that's raised the most questions about scale and materials among city officials, the architects say.

"I think that's our biggest challenge," Clark said, adding that the design is still being actively worked on.

The architects have also decided to construct the arena completely above ground, which presents additional challenges, including creating a welcome environment for pedestrians. It means the whole volume of the building is visible, making it taller and tighter to the edges of the site than originally hoped for.

Proximity to the water table prevented the below-grade approach. "It was a multi-multimillion dollar challenge," Clark said. Still, the arena will be shorter by about 25 feet than its predecessor, the BMO Harris Bradley Center.

Inside, the arena is designed to accommodate a variety of events, from basketball to ice shows to rodeos.

"I think the multipurpose arena is the most complex thing we do," Clark said of Populous, a Kansas City, Mo.-based firm that specializes in sports architecture. "They're like a Swiss Army Knife."

The lobby is a soaring 90 feet tall, meant to be a place of occasion and people watching, with grand staircases flanking each side. Every level of the arena opens up into this space, offering city views. Columns are angled to give the lobby a more dynamic feel.

The interior is designed as a machine to generate revenue for its owners, while providing fans with more social spaces. There are open bar areas where fans can grab a drink and still see the game, various levels of specialty suites, function spaces, exhibit areas and what the owners hope will be a high-energy club perched at the top of the tall lobby with an outdoor balcony. Many of these spaces and others are ripe for sponsorships, the architects said.

The 17,500-seat bowl is a blend of the geometries used for hockey, typically long and rectangular, and basketball, which is usually short and square. The highest seat in the new arena will be considerably lower than the upper seats at Bradley Center, and fans will always walk down to their seats. (The Milwaukee Admirals, though, recently announced the hockey team will move to the UW-Milwaukee Panther Arena in the fall.)

The Bucks hope to break ground on the arena in July, though no firm date has been set. The arena is planned to open by the start of the 2018-'19 National Basketball Association season. The plan is scheduled to go before the City Planning Commission on April 4.