Build and install a cedar bat house using the free woodworking instructions at DIY Network.
At the link you can download the free woodworking plans to build a bat house for your backyard.
This is a link to a Google 3D SketchUp drawing for a bat box designed to slip over a 2.5 inch O.D. pole. You will need the SketchUp software to download this drawing and its freely available online.
This bat box house plan has been successful in attracting nursery colonies of little brown and big brown bats. Bat roosting requirements are strict, necessitating adherence to construction details. Free plans at Wisconsin DNR.