Designing my deck with only 2 posts, allowed plenty of space for a shed. the first stage of building my shed was to build the roof within the joists of the deck. this stage took a long time and a bunch of thought. i decided to build an angled trough system with curved sheets of aluminum flashing.. How to build a shed under my deck 12x20 storage shed plans free how to build a small metal storage shed floor garden shed plans diy building plans for a 10 x 8 garden shed free plans timber frame shed barn wood is the most beneficial material to use for building your garden shed. roofing shingles should supply for the roofing.. Building a storage shed under your deck is a perfect way to maximize on this otherwise useless space. now your tools and equipment will have their own space. and maybe you can free up some garage space by having another storage area for your tools and equipment..