Well, Ceres is approximately 940km in diameter, which doesn’t fit either. It could, I suppose, be a stupidly huge space station along the style of a von Braun torus, mounted on the dwarf planet Ceres via some gigantic bearings. But the gyroscopic effects of Ceres’ rotation would be horrible, and Ceres’ gravity is enough to make things awkward. It would be easier to build a space station nearby and mine Ceres for materials. I think this has to go in the “sloppy research by the author” box.