You could build rings around rings. A couple of the designs on that page have multiple 'floors' in the same ring. I suppose those could be built incrementally in either direction (stacking new rings, or adding another floor to an existing one).

I think my train of thought makes a bit more sense for moon and asteroid bases rather than free-floating orbital structures. And asteroid bases - on the right asteroids - are probably going to house most of the people.

The ISS design definitely doesn't scale up. Everything off axis is a lever arm and the bigger you make it the more the whole thing tries to twist itself apart.