It is recommended that compartments be enlarged by closing alternating entrance holes and opening alternating compartment walls. So that martin house compartments are 6" x 12". For plans to build this Purple Martin bird house click the button below.
These free purple martin bird house plans provided graciously by Purple Martin Landlord John Balga of Ontario, Canada. This file is a full color, step by step, 39 page pdf file and may take some time to upload.