Here are three home-made designs. The top two are made of re-cycled clear plastic. These sharply limit infected breath from getting under the face shield. The plastic is not perfectly clear, but adequate.
The type above is made from a salad green container. It has walls on all four sides. It can easily be flipped on top of the head when not needed.
This type is made from a clear plastic soda bottle. It wraps around the head; has the curvature of the top of the bottle under the wearer’s chin and a foam head band.