So, after you build this Bat Roost, how do you tell the local bat population that you're open for business .. asking for .. a friend, purely for .. educational purposes.
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.
A friend of mine loves being in his backyard but hates the mosquitoes. He heard about this bat roost thing and installed one about 5 years ago. It has not attracted a single bat.
I guess like any other animals, bats will seek places with other bats, or where bats lived before.
The best option would be to procure a pair of domesticated bats and put them into the roost, I'm not sure if it's even legal.
The next best choice is to acquire a few kilograms of bat shit, and spray it all over and inside your roost, so it smells like bat.