Aircraft carriers, while we think of them as huge ships, aren't really all that large if you want to spend a lifetime on board one. Habitats have to be huge in order to not make the inhabitants bored out of their minds.

To put it into perspective, a 100,000 ton carrier houses around 5,000 people in tight quarters (the flight deck is just under 5 acres). and needs constant tending and provisioning for supplies. As an analogy to a space habitat they also make a kind of sense since they also have to house flying craft. There are only about a dozen carriers in the world at this size...or about a million tons.

Hollowed out asteroids with internal habitation spaces on the order of hundreds of internal cubic km would probably provide enough diversity to keep generations reasonably happy. The hollowing out process could supply raw material to space-based factories that would then build more habitat things and inter-habitat ships. Capture a couple comets and you have water, oxygen and other things. A small asteroid, something like 243 Ida has a total volume of over 25,000 km^3. Even if a couple km of shell were left, we're talking millions of tons of raw material.