Joe Johnston’s sketches for the Millennium Falcon. The cockpit of the Falcon was actually sawed off the original Pirate Ship model.

The design was changed to look more like a hamburger. The mandibles on the front of the Falcon were meant to be practical. From the book Making Star Wars:

 “We justified the mandibles by saying that they could be a freight-loading area where your cargo goes in,” Joe Johnston said. “Something comes out and grabs the freight and takes it back into the ship.”