First, figure out how much hanging space you need versus drawers or shelving, and also, what types of items need to be stored. You can fit a lot into the space with double-hung rods, as well as special hangers that hold clothing stacked rather than side-by-side. You may want to put your ideas together in a sketch, then take it to a closet design place or a contractor for installation. IKEA and others provide design assistance for customized closets.