A rolling roof, lots of natural light, more concessions, and separate levels — one for departures and one for arrivals. They’re all part of the conceptual design unveiled Wednesday for the new $1.1 billion terminal that will be built at Pittsburgh International Airport. The new terminal — tucked inside of the C and D arms of the airside building — will be used for check-in, security, and baggage claim. There also will be a large “meet-and-greet” area where visitors can wait for arriving passengers.