These types of skylights are typically mounted on curbs on flat roofs. The skylights are available with a variety of slope or pitch options. The skylight takes a pyramid shape over a square opening and is identified as a Double-Hip over a rectangular opening.
Rafter placement and glass size are determined by the geometry created by the combination of the relationships between sides and the desired slope. Multi-sided pyramids are available over six or eight sided openings as well as over irregular multi-sided opening in all sorts of configurations.
Skylight pitch is generally determined by other architectural conditions or aesthetic requirements.