A very simple form of continuous ring-shaped habitat is the torus; the classic design shown is the so-called Stanford Torus, which uses mirrors to illuminate the internal surface through a transparent roof.
The original proposal for this type of colony was made in the Information age at Stanford University in the USA. The design called for a torus one 'mile' (1.6 kilometers) in diameter housing 10,000 people.
In this image, of Chih Nii habitat in orbit around Penglai, the mirror collecting the sunlight is at the top, reflecting light to a semiconical mirror in the centre of the torus. Beneath the torus in the image is a radiator fin (introduced to cool the habitat because of the excess of collected sunlight), and two photoelectric arrays (of course the entire structure is in zero-gee except for the rotating torus itself, so has no real 'top' or 'bottom').
Tech Level: Stringtech 4