This box looks complicated but it's actually quick and simple to construct. The entrance hole is large enough for sparrows, but you can size it for any bird you choose.
Mount this mailbox on a post 8′ to 12′ high. Be sure the mail carrier doesn't try to deliver some mail!
Cut out the parts according to the cutting list. When cutting the entrance hole, drill the round part of the hole first. Draw the squared bottom of the hole and cut it using a jigsaw. I made an arched hole because it matched the mailbox shape better than a round hole.
Nail the ends to the bottom. Nail one side to the bottom and ends. Attach the other side with screws so you can remove it when it's time to clean the box.
Attach the top strips with nails. Start at the top of each side and work your way up. Fit the final strip, if necessary.