With the Polyroof tool in ArchiCAD 15 there are 2 ways to make a Hip End into a Gable. You can move the apex of the hip until the end is vertical. This does the trick, but it’s not the best. You get no overhang for the gable end, and you’ll get additional nodes added
The typical process for a project would be Sketch Design > Developed Design > Construction Drawings (add your own names as necessary). Generally the development of the BIM model will also follow this time line as well as more detail is added and resolved. A sketch design may be comprised of the primary elements Walls,