Maureen, here is one way a shed was painted with flowers. Hope this helps. Another lady painted old tire rims and hub caps and hanged them on the side of the shed and painted on the stems and leaves to have 3 D blossoms. That worked well too.
I used a stencil to paint a board to fake a window box on my shed, but you could use a stencil to cover the entire shed. There are really pretty patterns and vines that would work well. https://www.exquisitelyunremarkable.com/2018/08/faux-floral-window-box.html