Minecraft wiki entry for Roof_construction_guidelines, associated text: Other roof pitches need more effort, and not every pitch will look good at every roof size. Try to use a repeating pattern of two or three blocks that generates roughly the right slope; for example, a sequence of slab, upside down stair, stair, slab, upside down stair, stair, rises five blocks vertically for every seven horizontally. As a general rule, the more complex the pattern, the bigger the roof you will need before you can use it.