https://nestwatch.org/learn/all-about-birdhouses/

Pausing the woodworking aspect for a second, you might want to take a look at what nesting birds live in your exact area (a bird feeding specialty store can probably give great local advise) and what entrance hole sizes they need. There might be an obvious choice based on what you want to do with the existing hole, and it’ll drive the dimensions and placement of your final birdhouse.

My dad did a similar project years ago but it rarely got any interest from the birds in his yard - I think the bit of stump, hole size, and direction it faced weren’t a good combination.

Cool project!

I read that as "Helping me design the birdhouse" and I spent five seconds looking for the cat that isn't there.