re: #105 FFL (GOP Delenda Est)
Which had it’s own instabilities and needed unobtanium materials in order to construct. I think the Culture’s concept of “plates” made sense, but I think they also had an artificial gravity source technology to help make it workable.
At least you could spin the Ringworld - once you’d made enough scrith to build it! A Dyson Sphere would require artificial gravity.