Here is a hybrid structure of wood roof joists resting on a perpendicular steel beam. (The next photo looks at the column.) The wood members are rectangular, but the steel beam uses an H- or I-section, such that the material is distributed where it's needed: the flanges (top and bottom) and web (perpendicular piece connecting the flanges). This same economy of material extends to the cantilever, where the bottom flange disappears and the web tapers slightly.