Alright so lets say we are creating a ramp that connects to a bridge or something. Chances are it will look something like this.

Notice how the vertical wall extends from the ground. But let's say I want the vertical wall to also be sloped so it looks nicer. This cannot be done inside of scenery editor itself.
First, open a new FLD and insert your elevation grid. MAKE SURE TO INPUT THE WIDTH FIRST! (if you want it to be bent a little bit insert more than one grid on the z axis)

Now, add the thickness of your ramp (show/hide side wall)
Next, you're going to rotate the elevation gird to the slope of the ramp we want. So if we want a 20º slope rotate it 20º.

Now, you are going to save the FLD. DO NOT EXPORT IT AS AN ELEVATION GRID AS IT WILL NOT WORK. Open the FLD in notepad and find the TER part and do the following.

Now open up the FLD in scenery editor and you should have a sloped elevation grid with the vertical walls also sloped.

I also added support beams.

You are only limited by your imagination, there is probably lots you can do with these that I have not thought of.