Attached is a photo of a model. I went to Add > Mesh > Circle. Then went to edit mode, selected all vertices and extruded up. I can achieve the same result by drawing a bezier circle and converting to mesh first. I want to to the exact same thing with a square (at first) and then other complex shapes made from just lines. I'm unable to do a square. I tries grease pencil but just doesn't do what I'd expect it to. When I convert it to a bezier curve there's it always misses an edge and hence isn't a full square and it doesn't extrude like this.
I am not sure I understood what you want to do exactly and I am really new to it but I would go as follow:
- create a cube with the heigh/thickness (Z axis) that you'd like
- edit mode, face selection
- Deletion of top and bottom faces of the cube
You should arrive to this, and can always manage your object thickness on the Z axis in Object Mode with your Scale option/cursor. On the picture I am on Edit Mode, Edge select.
From there on, I would add vertex on edges as followed: Add vertex on edges
Like this you have a square bottom side and you can get more complex with the other top side.