I can't tell you much about this building. Not because I don't know, but because I'm not allowed to tell you.
What I can say is this is on Ministry of Defence land. It's design shares all the architectural style found across the country. In other words its square, made of bricks, sits on a concrete plinth and has a flat roof of the same material. It probably looks the same upside down.
At least modelling something like this is easy. Some Daler board for the walls and roof with Slater's embossed brick plasticard to cover. Or you could scribe the bricks yourself. My version is bigger (It held a battery box) and the door isn't as weatherbeaten, but they share a style.