I don't know that Founder's Hall is really a building, as Lindsey R writes. It's more of an atrium behind/inside of a building. Having explained that, it's a nice place to head to get some food or some shopping done, presumably either during your lunch break or after work, since it's right in the middle of downtown (and most Charlotte peeps don't really spend too much time in the downtown area unless it's late at night on the weekend).
Founder's Hall is a big, open area surrounded by fast-foody type places and shops like a little bookstore and a Bank of America store (weird). It's really bright and usually not that packed, though, so it's definitely a nice place to eat your lunch or grab a quick one if you're in a rush. Obviously, it's super accessible, so why not?
There's a little raised platform in there, too--try sneaking a meal in there. It's a great little area.