I came home to a small ball of fluff and wings wrapped up in the corner of my porch one day, so for gits and shiggles I put up a small bat box on a post against the trees nearby.
It took a week or two but I noticed it was in use when I went outside one night and saw one pop out of it.
Protip: be very careful about what you use to stain/paint it. Apparently they don't like the smell of those things. I didn't paint mine.