An unfinished attic or basement can be the perfect place to add closet space very inexpensively. Since both spaces have preexisting floors and perhaps a wall or two, this will reduce your costs for both materials and labor. Your new closet can be as large or as small as you wish, and can be finished to serve any number of needs. For example, installing shelves on one side of a large walk-in closet provides storage for most anything you need to store. Adding a rod on the other side creates instant storage for off-season clothing. If the door opens outward, all of the space in the closet will be usable. If you want to save money, you can leave the interior unfinished (for example, no drywall).