You can still use the old method of cropping the walls to a single roof, used mainly to trim walls in an angle.
If you are working in ArchiCAD 18 or older you already know that you can right click the wall and crop the wall.
However, if you are in ArchiCAD 19 you will find this menu if you select the wall and go to the menu Design>Roof Extras> You can either crop to the roof or undo the crops.
