The small touches make a difference. Some outdoor storage buildings come with French doors or cupolas. You, yourself can add touches such as window boxes, shutters, or weathervanes. Remember, you'll have to look at this outdoor storage building every day of your life for the foreseeable future: Your attention to detail could make the difference between eyesore and eye-opener. On a more practical note, purchase or build a pressure-treated ramp for easy access to your outdoor storage building.
Before installing storage units, lay down cinder blocks, concrete piers, a concrete slab, or at least crushed stone. But don't stop there. Make sure the supports underlying the floor are made of pressure-treated wood.