One of the pieces I fired recently was a birdhouse shaped like a smurf house. The roof was sculpted like a thatched cottage and the door was very organic and had a little lip of a thing above the opening. I guesstimated the size of the door with my thumb and then built a base designed to fit over most pointy posts. Finally I put a hole in the base so you could secure it.
I've had it stuck on a post out in the back garden on the path to the studio. I was seeing how the mounting worked and getting an idea of how it would be to have that house there. This afternoon I noticed that as I passed the birdhouse on my way back to my kitchen a chickadee flew to the birdhouse door. It landed on the sill, looked around and inside and then popped in. It turned around and popped its head out. Seemed to be pretty satisfied with the place. So, I'm feeling positive about that particular design and that particular house. I think I have to get beefier on the stake holding it up. If we got a wet winter it might drop the house. I also have to waterproof it with beeswax.