For roof support, trusses are easy to buy or build in a variety of configurations, and they make very efficient use of material. For example, scissor trusses allow for a sloped interior ceiling as well as a sloped roof. Gable roofs can enclose a large volume of space. One of the easiest ways to gain space in smaller buildings without enlarging the footprint of the building is to raise a gable roof slightly to create a half-story or a loft. Dormers are a little more complex to build, but they amplify the interior space and add significant amounts of light.
Shed dormers are easiest to build.
With straw bale buildings, one of the roof's main tasks is to keep as much water as possible away from the walls and base of the building. Generous overhangs are essential in wet regions, and in very dry regions with little rainfall, they provide shading from sun in summer, yet allow winter sun to enter. When walls are not too tall, keeping the eaves low will make the overhangs even more effective. For instance, where we live, a 32-inch overhang on walls approximately seven and a half feet high is not overly exposed to high winds and keeps the wall surface dry most of the time. Gable-end walls should have wider overhangs than eave walls, because the gables are higher.