A 12-by-12-foot shed is a good size, large enough to store lawn implements and other tools and supplies but small enough not to dominate a yard.. A 10-by-12-foot shed is the ideal size for a backyard shed to store all your lawn equipment or outdoor toys. it is small enough that it can be built with the help of only a couple of people.. The shed we built rests on a foundation made up of 12 solid-concrete blocks. the 4 x 8 x 16-in. blocks are arranged in three rows spaced 59 in. apart..
