If you're not concerned with aesthetics, You can't beat a shipping container for durability. Even the used ones come with a guarantee of water tightness. In terms of security they're tops. Along with that they're critter proof which comes in handy when storing any kind of feed, bird seed etc. A ten footer new will run about what you'd pay for a well built shed. Used in good to excellent shape $2500 to $3500 delivered. Every few years you spend a day with a wire brush and a can of spray paint to hit rust spots. The only down side is they're dark inside so you might spend a few bucks more for lighting. There's a place on Rt 148 in Brookfield that sells all kinds of containers.