The project is in its infrastructure phase, updating the neighborhood's utilities to accommodate the 150-story building. However, a spokeswoman for Dublin-based development company Shelbourne Development Group Inc. says construction on the tower, originally pegged at a $1.2 billion cost of development, has been stopped until the economy improves. A spokeswoman says the building will continue to rise once financial markets recover, and the target date for completion and occupancy remains 2012, as originally planned.

"We are slowing the construction pace down to match the economy," the spokeswoman tells GlobeSt.com "The decision was made to do that because the markets have completely seized up. When they are more fluid again, we will be in a very good position to move forward."

The spokeswoman says sales have continued to move forward, despite the tight financial markets. The tower, which sits on a 2.2-acre site where the Chicago River meets Lake Michigan, has had more than 30% of its 1,194 units sold since sales began earlier this year. Half of the units sold have gone to buyers from the US, while the other half have been purchased by international investors, she says. Units begin at $750,000 for 534 sf.

The building is expected to be the largest residential tower in North America and Europe, and will have the highest occupied floor in the world. Santiago Calatrava is the lead architect and engineer for the building, which company officials have previously said will cost $1.2 billion to construct.

"It's a very exclusive, private, one-of-a-kind building," the spokeswoman says. "When the market goes south, people look for strong investments that do not lose value. Some people will buy art, and this is somewhat like art. These are 1,194 completely unique pieces, and once you buy your unit, no one else will ever have that. Sales are not in a position of slowing down at all, as evidenced by the penthouse sale."

The spokeswoman would not confirm whether Warner paid the list price of $40 million for the penthouse, which occupies floor 141 and 142 of the tower. Warner released a statement about his purchase of the unit, saying he saw the purchase of the penthouse as "a unique opportunity to be a part of Santiago Calatrava's vision for the future of the City of Chicago."