If by "lexical," you mean a term to group the words according to their definition, then I don't find a good one for the first. "Shed," "cottage," and "building," are all enclosed, man-made structures. Is that what you're looking for?
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AnonymousHead, legs, mattressHyponyms for bed parts.
AnonymousShed, cottage, building.Hyponyms for what deadrat said.