3D Slope Problems

[bakedpotato]

So erm

I’ve been trying to make some 3D shapes, with help from the 3D slope guide. Unfortunately, that guide’s explanation isn’t getting into my brain for whatever reason, and I can’t make the top. Can one of y’all explain that last bit?

(If you understood none of that, I just need help finishing the top of this structure:

thanks)

[NotYoyo]

Try adding a background behind the slope, and then use a barrier with the same color to cover the preferred portion of the slope.

Very old screenshots from my map as reference: