I've got a flat roof garage with an extension built against one end. The extension is higher than the garage and the fall of the garage all goes towards the elevated wall. I'm trying to source some form of channel guttering that I can mount in the transition point between the flat roof and wall. or else the water will have nowhere to go. At one corner I have an exit point for water but there's no left to right fall so I feel the need for a channel all the way across is fully justified. Obviously there needs to be a fall on the guttering if I can get some. Anyone any ideas as I'm struggling to source something, which is a bit of a 'mare with the current storms.