sounds like a "ringworld" Larry Niven
the culture also used them -can't recall the authors name right now.
We may need some in ~500years when the earths magnetic fields playing swoppo games haha.
the Ringword was at 1 AU, half million km wide with rimwalls to hold in its atmosphere. It had oceans with replicas of mars earth and some alien planets as islands. The ringworld engineers (sequel) had sodded off and it was a little run down. It had shadow rectangles orbiting closer to the sun for night and day.