According to Cumberbatch, the set wasn’t simply the external structure of all the buildings, but much of it had also been outfitted with the working machinery that you would find in similar shops.
According to the exclusive clip, the set is 600 feet long and is made up of 60-70 fabricated buildings.
That’s the sort of attention to detail that, while it is rarely noticed by an audience, it does an important job of building the illusion.