My usual social circles were unable to help me find the answer I'm looking for, despite best attempts.
... Now some specifics to this problem: the kilograms per square meter of base of the buildings being suggested for the O'Neil Cylinder work out to a bit under 40,000 kg/m^2.
Assuming the walls would be made of concrete (taken from asteroids), since someone did walk me through the process of finding that concrete is strong enough "in general", but not specifically how much concrete is necessary.
One other note: concrete is usually suitable for the foundation of the kind of skyscraper style buildings we're dealing with when its on top of ground, and in conjunction with something to anchor deep into the ground; but neither of those are likely to be viable when we're dealing with there being nothing but empty space outside the walls.
... Before someone asks why this specific set of figures, the starting point for the original discussion was to recreate Shibuya in space. Kinda took the tallest skyscrapers in Tokyo as a baseline (after comparing them to the empire state building... Not an exact science there, but I rounded up a lot to leave some wiggle room)
I can't think of anything else that might be relevant to this question. But do let me know if I forgot anything necessary for this question. Also I'm sure someone's going to notice some other questions on what kind of dimensions the cylinder would have, so... Yeah, do point out any questions that sound interesting.