Construction of CityCenter began early this week when more than 10,000 cubic yards of concrete were poured to secure the 8 million-square-foot hotel and casino anchoring the project.

"There have been many changes — it's an evolving design," said Tony Dennis, executive vice president of CityCenter's residential division.

Many are occurring inside a two-story building of more than 100,000 square feet behind the Monte Carlo. The building is the site of constant meetings to discuss the design and function of CityCenter's multiple high-rise buildings.

It's an unprecedented collaboration of architectural designs and egos that don't normally work together. Rather than ordering up designs that fit a preconceived look, MGM Mirage executives are letting each architect have free rein to create their best work.

The problem is in integrating the buildings together so that traffic and people move smoothly. The 18 million-square-foot development — the largest privately financed construction project in the United States — is also being designed for maximum profit.

"We have hundreds of meetings a day," said Bill McBeath, president of MGM Mirage's Bellagio resort and the operations manager for the hotel and casino component of CityCenter. "This is a very large collaboration and a tremendous amount of work."

While most of the buildings' exteriors are finalized, MGM Mirage is still working on the look of an as-yet unnamed, 400-room hotel that will be run by Strip nightclub operators the Light Group and topped with 240 luxury condos.

Besides adding more than 1,000 condominium units to the final design, one of the most significant changes to CityCenter over the past several months is the selection of Chicago firm Murphy/Jahn to build one of the biggest groups of those condos.

Architect Helmut Jahn, known for his sleek, ultramodern designs and transparent-looking buildings, was selected after a three-month international design competition and has spent the past six to eight months drawing up a pair of condo towers that lean into one another.

From the north or the south, the buildings appear to be straight. But from any other vantage point, they lean dramatically, with the angle depending on where the person is standing.

"Creating two buildings instead of one brings in more openness and light," Dennis said. "It creates a sense of motion — no one stands in one place and looks at a building from the same place all the time. There's a dialogue between them."

Openness and light might not appear to be a hallmark of such a densely designed project.

Yet CityCenter is missing an entire condo tower that was part of the initial plan. MGM Mirage officials removed the tower, designed by Vancouver firm James KM Cheng, from the final design to free up more land for open space.

A model of the MGM Mirage's Project CityCenter is displayed during a news conference at the CityCenter offices on Monday. Photo by Steve Marcus

A key feature of the upcoming Mandarin Oriental hotel will be a "sky lobby" more than 20 floors up — offering dramatic, floor-to-ceiling views.

Two recent additions to the design team will be creating the urban hub of the project below the twin condo towers. Studio Daniel Libeskind, initially selected to redevelop the World Trade Center site in New York, is designing the retail and entertainment district. David Rockwell and Rockwell Group will create the streetscape — the arrangement of the retail shops.

The building housing the shops and other attractions will rise a few stories above the Strip, featuring an angular, jagged roof punctuated by skylights so that pedestrians can orient themselves to the surrounding skyscrapers. There won't be one boulevard like New York's Fifth Avenue or Chicago's Michigan Avenue but multiple avenues that come together at interesting angles, executives say.

It won't be like Caesars' Forum Shops — a self-contained mall with one storefront after another. And it won't be like the nearby Fashion Show mall, with one main entrance and no real streetscape, they say.

The desire to create a vibrant urban community with people working near their living quarters has been taken down a notch. Office space has been taken out of the equation because it wouldn't be as profitable as the international luxury brands and high-end fashion and entertainment houses the retail center hopes to attract.

MGM Mirage is still several months away from completing its 24-month design phase that began in late 2004. The interiors will start to take shape over the next 20 months, culminating in a late 2009 opening for multiple towers.

The hotel-casino building, the largest of the five, requires the longest lead time and is therefore starting first to see how it integrates with the overall design, McBeath said.

The Pelli tower is a radical departure from the typical Y-shape of the modern megaresort, the most efficient design for a large hotel. The building is actually made up of three towers, two of them positioned end to end in an S-shape.

These towers are designed to amaze, not to fit preconceived notions of profitability.

"These great artists have put ego aside — as much as humanly possible — to create something remarkable," Dennis said. "We have challenged them to be creative ... and to design something for 20 years from now."