Ringworlds require unreasonably strong materials. Dyson spheres are
worse.

But Alderson discs take the prize. they need some sort of reinforcing
to prevent them collapsing radially into a sphere. Worse, the amount
of material required would use up all the matter in quite a few solar
systems. Like hundreds or thousands. Probably more than that (I don't
feel like doing the math right now).

--
Leonard Erickson (aka shadow)
shadow at shadowgard dot com