Under Deck Ceiling Using Barn Steel Roofing Panels
The slope or pitch of the under panels can be at any degree that will shed the water. If you consider it as similar to a roof than according to Code: "minimum slope is 1/4 inch vertical in 12 units (2% slope)" and ideally :"1/2 vertical in 12 units (4% slope)". This is for metal roofs that have a sealant between their lapped seams. My only suggestion would be to remember to use the same metal fasteners as the roof and get the type with the neoprene washer below the screw head. Also depending on the roofs profile pick-up similar support backing (i.e. wavy board).