But good catch. I never saw that before. Perhaps it is a Britishism. In the US, we often name buildings for their streets like this:
"The 90 West Street Building is an extraordinary building - for its architecture, and for surviving 9/11. But to begin at the beginning: The West Street Building was built as an office building for shipping and rail companies..."Maybe Orwell was shortening the name of a building (the "West Street Building") to just "street building."
Maybe the typesetter made a typo.
I’d make a good proof reader. A lot of news websites sure could use one too, even the big ones.