Many people who want to maximize storage space choose to enclose the area under their decks. This is also a good way to prevent wildlife from taking up residence there. It works especially well with decks that are built with significant clearance from the ground.
The gap under a deck is very appealing to animals seeking shelter. Enclosing the area helps to keep out wildlife such as raccoons, skunks and opposums. To enclose the area beneath a deck, screw sheets of fiberglass or corrugated metal to the bottom of the deck, then install wood lattice around the exterior. Make sure there are no animals living under the deck before you enclose the space.