Part of a set of components which may be assembled in all sorts of ways to create a wide variety of stone buildings from simple farmhouses through posher urban terraces to more complex villas, hotels and even palatial manors without putting undue strain on system resources because the same basic units may be used again and again in various combinations.
Here's a rear extension for use with the double main unit: a third of it slides inside the middle of the rear of the main unit, as shown iun the screenshot: turning it through 180 degrees will give a reversed window layout for variation.