There are ventilation and drain holes in the top and bottom, respectively. As nesting material, broken bark is generally preferable to sawdust or shavings. Pine needles and leaves can also be used. Straw or hay, which support toxic fungus, should not be used. Some recommend this debris be cleaned out every year, but in the wild the owls build up thick deposits with no ill effects, and its ammoniacal odor tends to repel ants and flies.
Good ventilation is important both for cooling and odor dissipation.
An open fight path to the entrance is desirable ,as is much shade as possible. Barn owls have nested twice in one season in another barrel in a similar tree location at a ranch near Lake Casitas, California. If rope is used it should be UV resistant. Galvanized wire will last for a long time, as will the polyethelene barrels, which are preferable to steel barrels. The latter are heavy overheat the owls in climatic extremes.