43 pages of 12×12 gambrel roof shed plans and more for only $5.95 instant download and email support for building with these small barn plans.. This step by step diy project is about 12×12 barn shed plans. if you want to build a storage shed in your backyard that has significant space for many items,. Plan # 3342 is shown. these storage shed blueprints allow you to build on a concrete slab see our free on line construction guide for more.