"Large users have a lot of options, and they can make deals on space today," Goodman said.

Kent Ilhardt, executive director of Cushman & Wakefield's Downtown office, said it may be possible to use caisons that once supported the US Gypsum building at the Manulife site. Ilhardt, whose company was involved in the sale of the property to Manulife, questioned how the reported design would fly past the City Council and planners.

"It's interesting he'd build the first 12 floors without offices," said Ilhardt, referring to the reported plan to build the structure on a platform supported by 120-foot columns. "I don't know if the city would allow that, or if the tenants would like it. They must be putting in a false curtain wall." Rich Curto, chief executive officer of Prime Group Realty Trust, likes the reported design. "I think it's a unique concept of trying to avoid a potential view problem with the lower floors."

Officials from Lohan Associates, identified as architects for the project, were unavailable for comment.

Ilhardt also questioned whether Buck's due diligence would result in the developer going ahead with a project creating further competition in the office market. "Does the demand keep up? Does the absorption keep up? Does the economy keep up? We're all looking at the same picture," Ilhardt said. "I hope it's not a repeat of an ugly cycle, but I don't think it's going to be a repeat of the overbuilding we saw in the early '90s."

Despite Ilhardt's reservations, he's among those who aren't ready to bet against Buck. "Certainly he's a quality developer with the track record to make it happen," he said. And Curto suggests Buck will be required to have more than a few ducks in a row before the projects moves forward. "One of the key things to do is to talk to lenders, and they're not going to be involved with any buildings unless they're significantly pre-leased," Curto said.