According to Mr Welch and his book, once you've painted a roof and then picked out individual slates, the modeller should dry-brush the surface with a slightly paler mix of the base colour.
I mixed up from Humbrol 66, let down with a little 27, picked out a small, knackered, brush and worked the colour over the surface. To tone down the picked out tiles, I found quite a bit of paint needed application. Even then, I think I probably should have been a bit more subtle with my highlighting of individual slates.
While I was dry-brushing, the top of the chimney received a little tickle too although this will also get a dose of weathering powders as part of the next stage.
After this, the door, window and guttering have been painted. The last was in Railmatch weathered black which yet again, dried with a satin finish. Why isn't it matt? At least a blast of Dullcote sorted that.