I agree with that!
Those are exactly the points why I would never build with a BT. If you get the "wrong" one, there are tons of such points on a house that can be debated.
If my architect hands that over to the tiler or even puts it out to tender without coordinating with me what is ceiling and what is wall, he'll get trouble from me, because that's what I have him for.
If he now wants the tiles on the sloping roof, they'll probably cost twice as much as the others.