I found this photo of one of my low relief warehouses/sheds under construction. As you can see, the main structure is built out of styrene sheet. It's based on a photo of a prototype at Dingwall.
You can also see my method for representing the corrugated-iron roof. I glued a sequence of lengths of wire to a piece of plastic with suitable spacing. To produce the sheeting, a piece of aluminium foil is cut from a suitable piece of scrap food packaging (shown left). This is thicker than usual kitchen foil, helping the rigidity of the finished sheet. It is pressed by hand over the wire former with the help of a fingernail in each groove. The resulting sheet of "corrugated iron" is then glued on to the building and painted.
Below is the finished building in place on the layout (the green building). Using metal foil rather than scribed plastic --which I had previously used for the goods shed roof--allowed me to model the exposed end of the corrugated sheet, along with the collapsing gutter!