While a final tally has yet to be determined, last month's tornado did about $100 million in damage to the Georgia World Congress Center, the head of the facility said Thursday.

But through speedy efforts to make the building usable, the entire facility will be open for the first time April 28, Dan Graveline, executive director of the convention behemoth, told members of the Atlanta Convention and Visitors Bureau, which markets the city as a convention and tourism destination.

ACVB President Spurgeon Richardson praised Graveline for the quick work.

"If I had gold stars, I would give you two for that," Richardson said.

The cost estimate reflects cleanup immediately after the storm as well as reconstruction, Graveline said.

"In order of magnitude, it will be around $100 million, plus or minus," he said. "If all goes well on the construction side, it could be a little less."

The GWCC is self-insured through the state, and early estimates are that the repairs should be covered, state insurance officials have said.

The $100 million price tag is about the same as an early estimate by Georgia Insurance Commissioner John Oxendine.

The almost 4 million-square-foot convention center was among downtown buildings most damaged by the March 14 twister.

Roofs were ripped off, water cascaded down stairs and carpets were soaked by a sprinkler system tripped by the weather. The tornado passed directly over the massive complex.

GWCC staff had to move some conventions to other locations within the GWCC or to other sites in metro Atlanta. At least one group canceled its Atlanta trip.

Graveline said total costs could change because the work is being bid project-by-project.

Still to come: a new roof over all the meeting rooms in Buildings A and B and over half of the exhibit halls in Building B.

To make the building usable, temporary carpet has been put down in some areas, but it eventually will have to be replaced with permanent carpeting, Graveline said. And work continues on replacing more than 2,000 windows shattered by the storm.