You can't slope a room (floor) but you can use a triangle for a sloping garage floor or a ramp. Alternatively you can use a very wide and low wall, from 0.1 to 4 inches on the other end.

A sloping ceiling depends on what king of ceiling you want. The most common way is to use a box that you tilt. If you need a hole in the ceiling: first create a wall the size of the ceiling and insert a service hatch where the hole must be. Export wall and hatch, import and tilt.