The world's largest unsupported roofspan is really Boeing's 777 factory at Everett, WA. This factory has production lines for two 777 aircraft, one 747 and one 767. FOr obvious reasons, there are no supports in anywhere in the interior the entire roof (it is entirely supported on a struss that sits on the four walls) The roof covers a total area of over 4,000,000 sq ft.

It is the largest single space under one roof in the world.