Ringworlds are cool and all, but Niven Ringworlds. Those are the size of solar systems. And THEY are 𝘤𝘰𝘰𝘭.
A Niven Ring is actually two megastructures, an internal ring of orbital shades to simulate a day-night cycle, and an outer ring for habitation. It would be 600 million miles across and a million miles tall. The earth is 7,917 miles in diameter, for scale.
It would be so big that signals sent from one side of the ring to the other would take about an hour and a half to send and receive.