I think the castle is fine, size-wise. For rooftops, you can really get creative. Most of the time you get red tiles because that's the image of what European cities look(ed) like (some of them did), but if you look across the world, you'll see they can be green, golden, black, even opalescent blue (especially in the Far East). It should also be noted that in the Middle Ages roofs usually weren't tiled but covered with straw, so yellow with a golden hue would be appropriate there.