Learn how to a lean to shed roof. this is the 5th video in our how to build a lean to shed series. this video teaches you how to: -install lean to shed roof rafters. -install roof fascia boards. A lean-to shed is just that -- a shed that leans on the wall of a house, garage, or barn for support. lean-to sheds are great for storing mowers, cookers, garden supplies, and other things that need to be sheltered but do not need to be in a freestanding building. most lean-to sheds are built with. Frame the top-side wall of the lean to roof with 2x4 lumber. since a side wall of the shed will be higher than the other side, you’ll need to construct a small add-on wall for the side. the sloped roof of the lean to shed will allow water and snow to run off to one side of the roof without soaking into the wood. 2..