Minecraft wiki entry for Roof_construction_guidelines, associated text: Once a building is larger than about 15×15 blocks, it will begin to look increasingly strange (or, at best, barnlike) if it continues to have a simple roof. Large buildings usually have multiple roofs in different sections. Think of an English manor house with two wings as a common example. Trying to place a single gable roof over a building like that is likely to look ridiculous. It's at this point that more elaborate roof designs begin to be needed. The following Wikipedia article lists common roof designs and often provides pictures and diagrams: http://en.wikipedia.org/wiki/List_of_roof_shapes