Well, a plan is not just a little picture. The architect doesn’t make it just so you can neatly file it away and then build something different on a whim. The architect is supposed to fulfill his contract or return it. Or the OP builds as planned – I wouldn’t have a problem with the room height, but that the architect doesn’t get who the client is would annoy me. Rooms “lower” (I would rather say “not higher”) and a roof flatter pitched than desired and allowed would not yet result in a less beautiful house, but in the contractual relationship with an “artist” in my opinion the tail should not wag the dog. If I have tickets for a Mozart concert, I don’t want the conductor to suddenly decide on Beethoven. Here too, I have to be able to trust the expert not to do his own thing. Regulations must be followed, but not exceeded.