Pekka Janhunen of the Finnish Meteorological Institute, Helsinki, Finland has just posted a paper on the arXiv server describing his concept for a megasatellite space settlement in orbit around Ceres and constructed from materials from this dwarf planet in the asteroid belt. Ceres is chosen because of the availability of nitrogen and water needed for life support. A space elevator is proposed as an efficient means of lifting materials off the surface.
Janhunen works out the physics and mass budgets for a collection of settlements comprising the megasatellite, each providing 1g artificial gravity and a closed-loop life support system. The assemblage is made up of a collection of self contained rotating habitats which are interconnected and could potentially grow to house billions of people with 2000 square meters of living area per person. Each habitat would include soil thick enough to enable biomes with trees and ideal weather.
SSP covered another free space settlement concept by this author last April a bit closer to home at L5 in the Earth-Moon system. Janhunen discussed this duel-dumbbell design on The Space Show in May of last year.