What will President Obama and other leaders nosh on as they discuss the world's weightiest issues at the G20 Summit, opening today in Pittsburgh?

Well, that's top secret, silly. But what we do know is that there will be plenty of locally grown produce on the menu, about 5 percent of which was plucked right from the 600-square-foot rooftop garden (part of which is pictured below) at the David L. Lawrence Convention Center -- which no doubt should please the commander-in-chief and the missus, who've made it clear that local, sustainable agriculture is a priority.

Chicago-based Levy Restaurants handles catering at the ultra-eco-friendly, LEED-certified convention center, which the center's executive chef Dominique Metcalfe says is one of the world's largest green buildings.

Metcalfe says she got word they would be hosting the summit about three months ago. For the past week, she, chef de cuisine Robin Rosenberg (who flew into Pittsburgh Wednesday from Levy's innovations kitchen in Chicago) and about 40 other chefs have been going "nonstop" to get the grub ready. They expect to feed 4,000 over the next two days.

They have to keep mum on the menus, per White House rules, but Rosenberg says the world will be covered, culinarily speaking.

"We have about four different dietary laws we have to follow -- kosher, vegan, Hindu, Muslim," he says. "We have products from all over the world coming in just to satisfy everybody here."

For lunch, the chefs will offer oh-so-trendy bento boxes with deconstructed salads and sandwiches.

White House staff members already have toured the rooftop garden and are "just crazy about it," he says.

The Levy staff also will be sourcing from about 20 farms in the region.