I liked the Light Switch Cover - Key Holder design (https://www.thingiverse.com/thing:108988), but wanted supports under the shelf. So I remixed the STL using Tinker CAD. After adding the supports and getting a nice print, I noticed the cover was too narrow and short to cover the hole in my wall which was covered by the original switch plate. So I went back into TinkerCAD and extended the width and length without changing the switch holes dimensions. Now it fits great and covers the opening. Both normal and wide STLs can be found here. Please let me know your thoughts.
I made it with PLA. Works with no supports needed. If your adhesion is decent a skirt will do. No need for raft or brim.