I rarely if ever use the Roof Object; for anything but a very simple hip or gable I would pretty quickly reduce it to its component Roof Faces anyway, which are both easy to use and very capable. Once one Roof Face is create, it's easy to mirror and/or duplicate it as necessary, reshape it, and change its pitch and elevation as required to create a complex roof.
Regarding the 'math' of creating valleys and hips in plan: the angle of a valley or hip can easily be established by the two roof pitches. For example, the angle (in plan) of the valley or hip of a 7/12 roof and a 9/12 roof is 7/9. The angle of a valley or hip of a 2.75/12 roof and a 7.12/12 roof is 2.75/7.12. (The base run needs to be the same, whether it's 12 or 10 or whatever...).
To determine the intersection, in plan, of a conical and hip roof, the involved components can be duplicated and added together as solids. The intersection can then be traced from a hidden line drawing or, for more accuracy, the solid can be converted to a hidden line polygon and the desired intersection lines copied out of it.
HTH!