Where I work as an architectural draftsman, I recently had to draw a renovation that had a nasty roof on it. Not that nasty, but the question was, if a wall was removed, will the roof fall down?
By drawing in 2D you can make a few close guesses, so on the weekend I cranked up dear old Autocad to see what it would be in 3D.
The underlying drawing was not accurate, which accounts at least for some of the shoddy drafting!
More of an attempt to understand the structure.
Last thought....how much of a drama to produce this in Revit?
The positions of the rafters were found from a set of solid planes that were representative of the purlins layer, not drawn as individual purlins, but as a set of intersecting planes.