On Tuesday, the team renovating Key Arena in the hopes of courting an NBA or NHL team—led by Oak View Group (OVG)—announced the general contractors for the project. Skanska, an also-developer that’s currently building a tower at Second and University, and AECOM Hunt will be completing the work, which involves increasing the stadium’s capacity and decreasing its environmental footprint while keeping its iconic roof.

“Everything that you see from the outside of the building never changes,” Tim Romani of CAA ICON, which is managing the project, told the Seattle PI of the design by architecture firm Populous, “but it’s a complete reconstruction of everything underneath.”

With the Skanska Hunt announcement, OVG included a video with a partially-bisected view of how the work will be done, digging below the surface to expand the stadium’s square footage and capacity but leaving the exterior appearance untouched. When it’s all done, the arena will a 17,400-person capacity for hockey and a 18,600-person capacity for basketball.

The project was originally slated to cost $600 million, paid for by OVG and private equity, but some additional project upgrades brought the price tag to $700 million. OVG CEO Tim Leiweke told ESPN that various things raised the cost, including dedicated locker rooms for NHL and NBA teams and the existing Seattle Storm, plus 50,000 extra square feet for storage and the Space Needle view club that OVG showed off back in February.

With the current design, the arena’s interior will expand to 750,000 square feet.

An NHL team is expected to come along with the newly renovated stadium—33,000 people have already put down season-ticket deposits—but an NBA team is a little farther off. Still, the new Key Arena will host what the old one already does: Seattle Storm games and concerts.

The stadium could open in 2020.