Any time I see a small wooden box at a thrift store I grab it; plus my husband makes some for me. I'm talking about a place for the Mason bees - where she can lay her eggs. I've always seen a lot of them in my garden, but didn't know too much about them until I did some more research.
This first one, I used old wine corks cut in half for the roof (I've been saving those for years).
Here's another one we made:
In this photo, I hung three of them (facing east ) on some trellis that was already attached to a wall. Something is definitely using the tubes.
Here you can see the tubes being filled