Looked at your construction and it seems to me as if the crossbeams could be drawn with the method described above: use a blank file to draw the beam as a low wall 'laterally' so you get the correct angle, and then export-import-rotate selection. (Btw, you can control the angle of the end of the beam by adding connected walls that you do not export). But maybe I misunderstand?

As for the roof itself, maybe the triangle roof shapes in SF 3D models 330 can be of help?

ok