Terrain incline tool is on intuitive

I am new to the game, with only a few hours in it, but I find it really unintuitive how to start a slope from flat ground. Toggling the slope option on and off does not make a slope when it's on a flat ground. Also, being able to specify whether I want the slope going up or down would be very helpful. Maybe it would be something like you press the slope button once for down, and when you press it repetitively it toggles between up and down and forces the highlights to conform to the slope, starting from the height where it was originally specified.

If I understood corectly what you are saying, after pressing F, you can press R to change the direction of the slope. So you can start from the lower level, press R till the slope goes up a d then continue to the higher level