This shape sadly does only make sense with Drawn mode but it would make it much easier to build shapes that aren't aligned to the block grid.
I think this shape is best explained with a picture:

The golden bits are the points the drawing would start/stop.
The walls thickness should be configurable with the alt-menu, the Direction should have the effect shown in the picture.

If anything is not clear to you or not clearly formulated, please ask.

This is a very good idea, and I agree that it could be quite useful. I'm working on an imaging tool right now (it converts images to chiseled blocks in the world), but I might try to implement this after that's done and released.

I'm always glad to get suggestions. Thank you.

This idea would be very useful. Similar to this, i would like to be able to draw 2d and 3d lines. Maybe 3 point triangles? Thanks for the great work!