We haven't done many scratch built buildings, but we did use the Jigstones system to mould blocks and panels in cement,
I don't know if it's currently being marketed and I don't have any pictures of our buildings, but the cast blocks look like this:
Moulds are like this, doors and windows would need to be cast in plastic,
Edit - It turns out they are available again and it looks like they have added some roof moulds to the catalogue. I'll need to have another look at what I have in the drawer.
Bei Modellbau Heyn finden Sie schöne Details für die Gartenbahn. In Spur 2 gibt es Bausätze für Lokomotiven, Wagen, Gebäude, Gleise und vieles mehr.
www.modell-werkstatt.de