Maybe a carport instead of an expensive garage will suffice. We also have about 6x9m and separated the rear 3m with a wooden wall, which is now our garden shed (bicycles, lawnmower, etc.). You really can't make up a utility/storage room like that; what contract status are you currently in there? You would need a lot of lighting in the hallway so you don't constantly bump into this protruding stair extension; it looks as if copying it went a bit wrong? For the guest WC drawing, you either have to slap him or force him to live there himself with only that bathroom. If I were you, I would urgently get graph paper and draw all these things in exact centimeters and look at certain distances and measurements in my current apartment (distance toilet-sink-shower, etc.), then many things will become clearer. Nobody needs a terrace of almost 43 sqm, that's nonsense. Apparently, he rolled the dice for the windows; the one alone in the office is like that and not really feasible in any somewhat affordable way either. The ground floor is not necessarily spacious, but that is not necessarily bad if it were planned sensibly and cleanly. An 18 sqm bathroom upstairs, bigger than the living room—is that a gym? Oh dear, that also seems like it was rolled dice to me. I also don't understand the necessity of the two flat roofs, which certainly incur significant costs, while at other points living space is tight. Glass palace in the bedroom? Can you use the flat roof as a balcony? There, several thousand have already been sunk into railing, sealing, etc., without noticeable added value for you. I think he simply can't do it better, and further attempts would only consume more money/nerves; I would definitely stop that because it won't suddenly get better during construction. You want to build a nice house and get something like this, that annoys me. Almost everyone here has/had trouble during construction, so it is always just a question of when it happens to you. I definitely do not want to discourage you but rather encourage you not to accept that. You are a young family and deserve better—you are understandably not happy with this!