I make these custom owl boxes/houses myself and I always keep stock of these on hand. These are made from solid pine lumber. These are well ventilated, with vent holes on the upper sides and bottom. It also has a removable front hole plate for either a 3" hole or 6" hole depending on the Owl species in your area. Also, upper side panel and bottom panels are removable for access is needed.
This is my design but I can build any style you may want.
Charing the outer is also available if interested for an additional charge.
26"H x 11.25"W x 12.5"Deep/22" Deep including tray.