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.
If the clutter on your property says one unit isn't enough, but your wallet disagrees, supplement your main unit with one of the less expensive, smaller models. There are three main types of such units, all of which go by descriptive names. "Corner sheds" are made to fit precisely into a corner and run about 3 feet tall by 3 feet wide by 2 feet deep. Meanwhile, either a "vertical shed" (5 x 3 x 4) or a "horizontal shed" (3 x 5 x 4) may be just the handy outdoor storage building to fill your need for additional space.