I needed to replace my older thermostat with a Nest thermostat and the plastic cover plate that can cover up the old location on the wall (usually due to not being painted behind) was not quite large enough. I whipped up this thin plate and it came out nice - now it hides the paint line where my old thermostat was located. The Nest is much smaller. It looks decent, painting the wall would have been the best option, but that can wait now. Hopefully someone can find it useful as well...
I used PETG solid white for this part. I find PETG likes 260c with 60c bed temp - works best for me. This is a pretty simple part, you can make it however you want it should be fine....