We build our own construction bat houses. Most are for large colonies of bats. Bat condos are what we build for several hundred or more bats. Here are some photos of a state park we did for Tomlinson Run State park in W.V.
All bat houses need to be constructed according to the colony size at the moment and additional size considerations for birthing expansion for years to come.
That is if we are talking about a maternal colony in general. I believe these were 36" x 24" x 8". They were quite heavy to install.
Photo from the ground looking up into the baffle areas. Lots of guano to clean up below these large units.
These bat condos were built for colony expansion for many years to come.