What do you do with 100,000 square feet of empty building space? That's a question the owners of the Railway Exchange Building are putting to the public at an event on Wednesday night.

The 21-story building has a lot of empty space since Macy's has downsized its local offices -- and plans to further downsize its current downtown store from seven floors to three in 2011.

RKMerlyn Development and Bruce Development, the current owners of the building, are soliciting ideas for what to do with the vacated floors. A fashion incubator for local designers has been one idea that has been gaining some traction and has generated some buzz in the local fashion community.

A gym (including a running track) and a space for designers and entrepreneurs are some of the other ideas already submitted to Ideabounce, a program by Washington University's Skandalaris Center for Entrepreneurial Studies, which is hosting the event.

About 15 to 20 people will present two-minute pitches on Wednesday night to a panel of judges. The audience and judges will select five winners who will receive $100 each and an invitation to dinner with the judges.

The event will be held at 5 p.m. at the Macy's store in the Railway Exchange Building, 601 Olive St.