[H]is phenomenologies are phenomenological ontologies: they look at the coherence of something appearing precisely as how it exists, in its being (taken intransitively, as be-ing or is-ing: Levinas said helpfully once that Heidegger's contribution to philosophy is in restoring an intransitive character to being). So the being of building is a sort of coherence, its remaining proper to itself as a phenomenon--but doing so not in the aspect of how it looks or feels, say, but in how it exists, how it just remains there in its activity as an activity, how it "just works" as we like to say, implying some process but at the same time implying that it just does this process in being typically itself. So he's looking at the way building is properly being building.