Ring Colonies are colonies that can become reality from Halo Reach's fictional ring colony on a map called forge world. This can become a reality. If one were to be built around the Earth, it would have to be faced upwards, not faced at the Earth nor away from the Earth. If that were to happen, it would always be night time near the equator. Ring Colonies can support billions of people depending on its width but it would currently be impractical.
Although it can be possible, but it would need a huge dome to cover the artificial atmosphere.