Dom,
frankly, I don't know yet. My first project was very similar to the one that Grimm built.
I have technical requirements with 4 13cm long roof sheets, I can have a tower of 8cmx8cm, so the remaining roof length is about 18cm.
I can put the tower on the far end, or in the middle. I don't know if I should texture the walls with plaster or with stone or both.
Olivier