Bats are the only mammal that can actually fly. Most bat species are insect eating machines, eating up to 50% of their own weight in insects each night. My bat houses are made with 2-3 chambers made from wire screening so that the bats can grip and hold. One or more of these compartments will be the nursery roost. They like a warm nest, so the house should be black to absorb heat and should face the sun. If you have a problem with mosquitos, you should have a nest of bats to feed on them. The first season you will only get a few bats who will breed in the fall.  Bats are nocturnal, in most cases you won't even know they are there. Bat houses do not open for seasonal cleaning.
718bat chambers
Note that I build my bat houses
with (3) three chambers. If bats are birthing they will use 0ne chamber for their babies.