This existing answer's sample file has a stage (I don't know what it is called) which seem to have 3 faces, but the middle one is curved.
I had learnt a way to create a stage like that on YouTube, but the procedure was:
- Add a plane
- Extrude one edge perpendicularly
- Add a bevel between the two surfaces
- Use the mouse wheel to create lots of angled surfaces.
I wonder how the person created the same stage with only three faces.