Although the developer, Alter Group, declines to put a number on the cost, a reasonable estimate would begin at $100 million. Achieving Leadership in Energy and Environmental Design status, superior infrastructure and other design elements will increase the cost compared to other class-A buildings, Alter Group senior vice president Matthew A. Ward says the incremental costs are "less than you think." They also are likely to be recouped by tenants who see greater worker productivity in an environmentally friendly building with flexible floor plates and energy efficiency. "The costs might be 5% to 10% more, but the returns on the investment are 10-fold in terms of worker productivity, quality of life and economic sustainability," Ward tells GlobeSt.com.

Ward's task now is finding at least one tenant willing to take at least 50,000 sf to anchor the building, but he has identified "two or three genuine prospect." Although the East-West Corridor remains soft, as total vacancy in the largest suburban submarket starts the year at 25.4%, according to US Equities Realty, Inc., the highest in the entire market. However, the 93% of the 517,500 sf in Corridors I, II and III is leased, with 148,000 sf in deals signed last year, according to president Michael J. Alter.

"We feel pretty confident," Ward adds. "Not only are the buildings' locations attractive, but their infrastructures are superior."

Corridors IV, though, promises to be the most aesthetically attractive. Jahn says his design calls for the building's façade to be lit in green, blue and yellow at night.

"We want to advance the suburban office building," says Jahn, whose firm, Murphy Jahn Associates, won AIA Firm of the Year honors in 2005. His local portfolio includes the James R. Thompson Center, 120 N. LaSalle St. and Terminal One at O'Hare International Airport. "Corridors IV will create a true integration between human, natural and financial capital."

Ward tells GlobeSt.com his company could seek a permit this summer, with completion coming as early as late summer 2006. Alter Group has not decided whether to sell off Corridors IV or keep it in its portfolio has it has Corridors I and II, Ward adds. Atlanta-based Wells REIT bought Corridors III for $40.5 million in the fourth quarter, or $182 per sf.