Discworld

While Earth is certainly not flat, that wouldn’t stop people from potentially building a Discworld, a flat, cylindrical surface that would float out in space. Gravity on a disc would be the most complicated problem to solve. If you were standing in the center of the disc, gravity would point straight downward, as usual. But as you approached the disc’s edges, gravity would continue to point toward the center of the disc. You would feel like you were walking up a steep hill. You could try and solve the problem by varying the mass along the radius of the disc to compensate for the change in gravity (less mass at the center, more out toward the edges).

Learn more about it in the Digital Edition of "Megastructures: The Visual Encyclopedia" 

https://artofsoulburn.gumroad.com/l/qnntu