Bit of trivia; if you measure height to highest occupied floor or height to roof, then the Sears Tower in Chicago is officially the tallest building in the world. If you count height to top of architectural structure then the Petronas Towers in Kuala Lumpur are the tallest, and if you count height to tip of antennae then it's the World Trade Center in New York. The CN Tower is not classed as a building because it has no floors except the observation decks, however if it was it would win handsomely in every category so for what it's worth it gets my vote as tallest building in the world...