You know the space station we had up in the 70s. I know it was made out of a leftover Saturn booster, but that’s about it.
It was about 80 ft long and about 20 feet wide.
There’s an unmanned backup copy of Skylab 4 at the Smithsonian Air and Space museum. You can crawl through part of it (a connecting segment). It’s tiny, like a Jeffries Tube! I think there’s another one at Cape Canaveral.
You can see a diagram of the Skylab here. It’s part of the online book SKYLAB: A GUIDEBOOK. You’ll see that main module (“Orbital Workshop”) was 48.1 ft long and 21.6 ft in diameter (external size).
ISS modules need to fit into the Shuttle cargo bay so they are much smaller. The Destiny laboratory module, for example, is 14 ft in diameter and 28 ft long. But the ISS is composed of many modules so I’m sure the total volume is larger than the Skylab. The ISS also has huge truss structures for mounting solar panels and radiators.