Plywood for the main box (3/4" sides, 1/4" back, rabbet and dado joints). Cut the door 1" too narrow so I added a handle from cedar scrap. Shelves and sheet pan brackets are reclaimed bed slats, planed. Window hole is routed with plexiglass insert, my first time doing any significant router work.
First bake came out well:
The brackets for the baking sheet have a cutout to accommodate two bowls. My goal was either two bowls or two baking sheets.
An obvious improvement would be to install an under-counter outlet so the cord is less prominent.
Heating is from a 45W incandescent bulb (which was the hardest part to find). It's in the top of an old desk lamp. Adding an 8x8" pan of hot water kept the humidity high so I didn't have to cover the rising bread. Temperature/humidity logging is from an SHT30 (plus two DS18B20s) running Tasmota and reportig to HomeAssistant, viewed in Grafana. I expected to have to cycle the light, but just keeping it always on seems to give me the right temperature range.
That's awesome!
I can also imagine you contemplating the horror of having to drill a hole in that beautiful end-grain counter to route the power. If I may suggest something that you've probably already thought of a solution for: routing power from an electrical outlet for this case is not hard. You could add another outlet under the counter behind the proofing box, and chain it to the upper one. If you've never done it, it can sound overwhelming, but it really is very easy - much easier if you can temporarily remove the proofing box.