[Steve A]

Here's an interesting thing about "real" ringworlds that nobody has brought up. The total solar energy reaching a planet beyond the sphere world is exactly the same before and after the ring world is built, just shifted in wavelength. This is true even if the sphere world blocks all direct sunlight. Instead of a 1 million mile wide sun radiating at 7000 degrees K you will have a 180 million mile sphere world radiating at a lower temperature. The energy radiating from the sphere world will be mostly infra-red with no visible light component.
As a result of ring world construction, any remaining planets will have approximately the same temperature but receive no visible (to humans) light. Lifeforms that use IR may still be happy.

Steve