I want to try to make a wall with a sloping side. I found the slope options in the Modify screen of a wall. But it seems I can only make sloped walls that are wide at the bottom and narrow at the top.
Or you can draw the wall in its upright position, then use the CopyAsNewFurniture plug-in, then Export to OBJ format, then Import furniture and turn it 180 degrees during importing. See the Sloping roof manual (PDF) for more info on this workaround.