Dive summary:

• The Council on Tall Buildings and Urban Habitat (CTBUH), which is a combination of record-keeper, umpire and cheerleader for tall, supertall and now megatall buildings, keeps track not just of how high a building is but of how high the occupiable part of the building is.
• All the area in between, whether it's a spire or lights or broadcasting facilities, is referred to as the "vanity height" of the building, and that can account for a good chunk of the overall measurement.
• Looking at supertall buildings, which are any above 300 meters, or 984 feet, CTBUH calculates that the tallest building (for now), the Burj Khalifa in Dubai has 29% of its 828 meters unused, the Burj Al-Arab is 39% wasted height, and the Bank of America tower in New York has America's biggest vanity height – 36% of its 366 meters.

From the article:

The results demonstrate that many super-skyscrapers have surprisingly uneven ratios between habitable and non-occupiable space. ...