I want to have a worldwide superstructure, covering all usable land and all usable continental shelf. Assuming that the Burj Khalifa is about as high as we can go, how many people can I have in my world-wide superstructure?
The tallest man-made structure in the world is currently (2016) the Burj Khalifa at about 830 meters tall, with 154 usable floors, and about 300,000 sq. meters (3.2 million sq. ft) of usable floorspace. However, the Burj tapers off towards the top, so a mega-structure might have more space. Think of this as a "floor" estimate, hah!
Moreover, I want to spoil all the residents, so with the gardens, vast open atriums, pools and all that, each resident will take up 10,000 sq. meters (107,000 sq ft) of space.
Keep in mind that the Burj actually has much more space, it's just dedicated to maintenance, structural support, quake-proofing, etc.
Edit: Assume that food is not an issue: these urbanites are either kelp-farming the ocean, keeping the farms underground near the fusion reactors and anti-quake stabilizers, or growing it in orbital farms linked by space elevators, whatever.