Here's the space it needs to cover:
And here's the almost finished product. I still have to stack up the stone the rest of the way, but the door is pretty much finished here. Strap hinges, knob and all. Made from scraps and old parts.
I started by cutting and ripping some scraps all to the same size. The easy part.
Then I fastened the boards to the general shape of the door opening.
Note the unintentional mean eyes and flared nostrils in the center.
Then I was lost, but she told me to just put the rough door inside behind the opening and just trace the outline of the door frame onto the door. I did what I was told and it worked out swimmingly.
We didn't get pictures of the jig saw phase, which is a shame. That was the crazy part.