I don't use GW paints.
Yellow Ochre ,ochre, Ivory. and medium gray and or a raw umber wash over light gray spray primer. Any of the Palid brands of craft paint or artist acrylics will work fine for 1/10th the price of GW paints.
If you are going to paint over plaster skip the primer and thin the paint with Future floor wax and stain light to dark. Over primer paint dark to light.
Roof tiles. Prime with black. Then over spray red oxide primer. Paint dark to light with antique brick then terracotta.
Americana heritage brick and Craft Smart Red brick are also good base colors for the roof.
The dock building is pre-painted MBA. The building on the left was painted over black primmer the building one the right over red oxide primmer. I painted these so long ago I don't think I used a black under coat on the roofs. I would now.
I used Country tan, Desert sand, and bleached sand on the wall.