Thanks Robin... that's one good idea for the open space an for the water towers.
I used one of my wife's travel posters, which is made out of thin cardboard. Chopped it up into the shapes I needed, flattened them out a bit more, spliced them together with Smooth It (spackle after that dried up) and then painted them with Ceramcoat's Charcoal Acrylic after sanding. Grades were filled with Smooth It until it dried up and then Spackle - painted with the same stuff.
Lines will come next, followed by weathering of some kind with chalks and I suppose Dull Coat to seal it.