This site has some useful information for bat house plans to build. My experience would rule out a single chamber house for maternity colonies. I think the small bat house plan on this site would be a great start and give one a
good chance for success to attract bats. The house should be mounted and placed in a good location. Also it should be stained outside or painted with a latex paint to suit the temperatures in your area. I would suggest that you do a search to find BCI and other sites on the internet for information specific to your area. Also there are probably
bat forum members in your area that may see your post and give you some assistance. Welcome to the forum and thanks for deciding to help the bats.
Here is a link for you.
http://www.batcon.org/pdfs/bathouses/fof_bathouse.pdf This is BCI :
This is from the PA. Game Commission. I know the small bat house plan is a good one as I have had success with it for little brown bats in the past.
http://www.portal.state.pa.us/portal/se ... 397&mode=2