I used some new/old stock door trim/plinth pieces for the body of House #3. Some cardboard tubes finished it out with some board on top to keep them pressed down and in place.
I hope some of you will or already have built some mason bee houses or purchased some for your yard. They are amazing polinators that get more pollination done than most bees. Be sure to not use old wood that holes have been drilled into if possible. Over time, they are prone to contain and harbor diseases and pests which works against your success with mason bees and other similar bees like leaf cutter bees. Please use paper lined cardboard tubes (so they can be cleaned out) or trays that have been routed out. There are also many suppliers out there that can sell you these items to get you jump started on Etsy, Amazon or their own websites. Happy Pollinating!