Adding a lean-to to existing shed would be perfect! i could tuck it against the side wall, the only accessible wall. the slope of the original shed, however, put some constraints on the lean-to height, which would also impact the other dimensions. to get a usable height, the shed could only be 8-feet long.. Metal lean-to sheds - easy to install american made steel garages and building kits with easy customization options as per your needs. call now at (877)-604-2777. Building a new shed to house my riding mower or the honda pioneer. attaching the shed to the same building i built the lean to greenhouse to..