Shop size

What does everyone think? It will not be a storage area, just a work area. Building will have have a small area for our well storage tank. Only other thing it will be used for is to reload ammo. Only shelves/storage will be what is necessary, another words there will not be parts storage for everything, just what I am working on. Will be a pole building, and in speaking to a local builder he suggested a 12 foot sidewall, but I am not concerned to much about the height, just width and length. I am thinking 24' wide by 30' deep but what do you guys think?