The structure simply known as The City or the Megastructure in Tsutomu Nihei's Blame! appears to outclass everything else here.
It's a classically engineered structure (i.e. no quantum "there's an entire universe inside!" cop-outs) that extends roughly spherically outwards from the center of the solar system to a point at or beyond the orbit of Jupiter. It's constantly expanding, being built by out-of-control AIs. It's multi-leveled ("the megastructure" nominally refers to the constructs separating the levels but is also shorthand for the whole thing sometimes) and so the theoretical "habitable volume" is enormous, although in practice few areas have oxygen, or gravity, or lack of killer androids, or etc.
Nominally this makes it a Dyson sphere, or rather a series of Dyson spheres, but I'm not aware of any other work of fiction that portrays a Dyson sphere this large. It also has some elements of a Matrioshka brain, as some kind of computer network appears to run throughout it.