For nearly maintenance-free storage units, vinyl is the preferred siding. Vinyl lacks the visual appeal of wood, but if you own a house with vinyl siding, why not select a storage unit that is also sided with vinyl? However, vinyl will get dirty over time, making it even less attractive. Mold is often the culprit. Take into account the maintenance required to clean the vinyl periodically.
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.