Part of a set of components which may be assembled in all sorts of ways to create a wide variety of stone buildings ranging from simple farmhouses through posher urban terraces to more complex villas, hotels and even palatial manors, but without putting undue strain on system resources because the same basic units may be used again and again in various combinations.
A reversible dormer window pre-set at a notional correct height for the two-storey main units, although there's scope for variation.... Shown on the background model as well as separately on the right with both faces visible.