Good references
COLONIES IN SPACE, by T.A. Heppenheimer
THE HIGH FRONTIER, by Gerard K. O'Neill
NASA SP-413, SPACE SETTLEMENTS A Design Study
I favor the cylindrical colony design. As your spacecraft approaches the space colony you see the outer radiation shield. This outer cylinder orbits outside the colony hull and is 20 feet of mining slag thick. Inside the colony the radiation level is lower than on Earth's surface. The colony itself is a cylinder 300 meters in diameter, and 2000 meters long, the outer hull is of radial construction with steel bands 8 cm thick to hold the pressure and a deck of steel plates welded for air tightness. A central axis tube provides the strength to hold the end caps in place relieving the outer hull of end loading allowing the cylinder itself to be of radial construction. The central axis also provides a transportation tube to the outside as well as serving as the tension member holding the ends of the cylinder in place. Inside the colony there is a huge space available for habitation. Light weight inner cylinders provide living levels at 100 and 200 meters diameter giving you a choice of gravities to live in, and open spaces through these levels provide dramatic views. The inside of a typical urban shopping mall with more plants is a comparable environment. There are several differences however. One, because this world has a central axis, you can hang buildings in midair. I call it suspension architecture and it will be a prominent part of human life in space. Second, as you move from the outer hull level towards the central axis tube, you will lower the level of gravity eventually to zero, Space is just an elevator ride away. This will allow much lighter structures to be used near the axis of the colony, the architecture will become light, airy, and very innovative. Living in a low gravity environment will allow unique activities such as human powered flight, 3D football, unbelievable acrobatics, and health benifits for the aged.
A single colony on it's own would not be economically viable. If a several of them were linked together in a grid structure however, the resulting economic unit would be able to support a small economy. If thousands of space colonies were linked together with communication systems, transportation systems, and commerce into one massive nation, then that system would be the economic center of the solar system. It wouldn't be one giant city, but thousands of small communities. A small town life style with easy access to the conveniences of a nation.
With the resources of this solar system available to the inhabitants of a nation of Space, a viable population of several trillion people could be easily and comfortably supported. With a dispersed population that particular problem of planet bound populations know as extinction would also be avoided. As humanity becomes comfortable living in Space, thoughts could be turned to crossing the immense distances between the stars, not to look for habitable planets, but for resources to build more space nations.