To conveniently store drywall, paneling, plywood and other long boards, build a second wall out about 2 ft. from a shop wall. Behind this new wall you can store panels, or you can use the space to build shelves as needed to house long dimensional lumber. But build enough shelves for long boards so you don't have to unload a large pile to get to a board near the bottom.
Get at least three written estimates from contractors who have come to your home to evaluate what needs to be done. Be sure the estimates are based on the same work so that you can make meaningful comparisons.