The guttering does not actually require to have a slope as water will always find its own level. Providing the building is itself level water will flow out. As the guttering is 32mm deep, an inconceivably large amount of rainwater would be required to fill and overflow. House guttering on the other hand takes a fall into account simply due to the massive roof area, heavy flow and long guttering runs, in comparison to a typical garden building. Such a fall is typically only around 1/4″ over 10ft in any case, and guttering can flex more than that along its run!

However if you really wanted to lower one end (if roof is not level etc) then a small packing material such as a block of wood could be placed between the lower clamping part of the bracket and the building if suitable.