Natural wood is considered by many the most attractive siding for storage units. But wood exposed over time to water usually rots. Some woods, however, contain natural resins that make them relatively rot-resistant. Cedar is such a wood and very popular as a siding choice for storage units. But even cedar siding is not maintenance-free. Coat cedar with a UV-inhibiting sealer/preservative every other year to protect it from ultraviolet solar radiation. Apply a clear stain, as well, to help preserve its natural beauty.
Become acquainted with zoning ordinances, deed restrictions and building codes. Depending on your area, you may need a building permit. Building codes may determine how far storage units must set back from property lines and what materials are acceptable for siding.