Currently (Archicad 26) the roof tool allows modification of each plane, to assign eaves/gable/ridge/valley... etc. and to individually decide how the edges are cut.
In actual construction this is a complicated element and should really be defined using complex profiles.
The issue we have every time is at gable walls.
The roof thickness defines a visible line on the elevation, and the surface needs to be custom made to reflect the roof angle.
Might this thread from when the Railing Tool was first released help?
The 'eaves' etc is only used for schedules, so you can determine the quantity (could useful to know how many m¹ of gutter is needed etc).
In case you were wondering what functionality that currently has.
Until your wish is granted: it isn't too difficult to model most connection by adding 2nd roof with a different composite and using 'merge' to make the floor plan display correct.
We have no issues to generate sections up 1:50 scale without modelling too many extra elements this way.