There are a couple of artillery-style shells lying around here and there in Absalom, Absalom!, but otherwise the word is used almost exclusively either metaphorically or in the bones-of-a-building sort of way (along with an occasional combination of the two).
As the novel tells us (spoiler alert: moral of the story ahead), “the South would realize that it was now paying the price for having erected its economic edifice not on the rock of stern morality but on the shifting sands of opportunism and moral brigandage,” so the recurring imagery of denuded or decaying buildings is certainly apt—just a bit redundantly depicted.
Various structures are built (“he erected that shell of a house”), inhabited (“he lived in the Spartan shell of the largest edifice in the county”), abandoned (“the store was now just a shell”), regarded with melancholy (“the house…but a shell marooned and forgotten”), revisited (“I went on up the drive…and reached the house, the shell”), plundered (“the rifled shell of the store”), acted upon by the elements and gravity (“the rotting shell of the house with its sagging portico”), eyeballed from a distance (“peering up the tree-arched drive toward where the rotting shell of the house would be”), and foreshadowingly described in the lead-up to the book’s fiery conclusion (“the house, the monstrous tinder-dry rotten shell”).
In a less architectural vein, Ellen Coldfield (not to be confused with her sister Rosa, better known as Miss Coldfield) is a character compared—repeatedly—to a butterfly, so she figures in such phrases as “some (even if invisible) cocoon-like and complementary shell in which Ellen had to live and die” and “[t]hen Ellen died, the butterfly of a forgotten summer two years defunctive now the substanceless shell” and “Ellen was dead two years now the butterfly…the bright trivial shell.” (Spoiler alert: Ellen dies.)
Ellen’s husband Thomas—I guess it’s true what they say about old couples growing to resemble one another—is also something of a hollow man: “he himself was not there…[t]he shell of him was there.” This being Thomas Sutpen, the book’s prime narrative engine, he who builds the house at the start of the first chapter that will wind up in ashes by the end of the last, it’s not unexpected that he is himself described as “the static shell,” “the sentient though nerveless shell,” and “the familiar dream-cloudy shell.” Maybe less to be expected is that four such references would occur in the space of five consecutive pages, but—presumably goes the thinking—when constructing the framework of your man-as-a-house analogy, better to err on the side of being well-reinforced.