I'm afraid I know nothing about this building other than it's part of Portsmouth's historic dockyard and is best seen from the harbour tour boat.
It is a very typical structure seen in docks. Look in any book and you'll see very similar buildings.
Not a bad prospect for modellers, the length could be tailored to fit the site. Windows are square topped and the roof is asbestos sheet, although this looks too clean to be original. I'd be inclined to keep the square "tower" at the end of possible as it adds a bit of character.