Ringworld Author:Larry Niven "I myself have dreamed up an intermediate step between Dyson Spheres and planets. Build a ring ninety three million miles in radius - one Earth orbit - which would make it six hundred million miles long. If we have the mass of Jupiter to work with, and if we make it a million miles wide, we get a thickness of about a thousand meters. The Ring... more »world would thus be much sturdier than a Dyson sphere.
"There are other advantages. We can spin it for gravity. A rotation on its axis of seven hundred and seventy miles per second would give the Ringworld one gravity outward. We wouldn't even have to thave a roof over it. Put walls a thousand miles hight at each rim, aim it at the sun, and ver little air will leak over the edges.
"The thing is roomy enough: three million times the area of the Earth. It will be some time before anyone complains of the crowding."« less