Try Bat Conservation International's "Bat House Builder's Handbook". It contains the latest research and designs for the highest success rate.
I have over a dozen bat houses and only two have not been occupied. The successful houses were usually occupied within 6 months.
In the Southern states(ie Texas), the most common bat house occupants are Mexican Free-tailed bats. In the Northern states, Little Brown and Big Brown bats are the most common bat house users.