Then I would question the builder and his offer before waking up with a hangover and having to cut back or finance more on the construction. I come to 240 sqm of living space with an open space and plenty of window elements, lots of recesses and projections, a hidden pantry, and everything that is good and expensive. That's just about 2600 euros/sqm. Plus the double garage. I see the planning more around 850,000 - if not even more. If you have that in your pocket, then you can gladly worry about the dark hallway. We received an offer for a two-story extension in a mid-priced region in February and were at 2900 euros per sqm (without having to greatly expand heating or similar). 100,000 euros for an extension that would have increased the planned living area by 50 sqm.
I see it the same way as the previous poster. There is not much to gain under 800k, standard equipment (plastic windows, concrete stairs, cheap doors, conventional electrics, basic fittings, cheap floors) without furniture.
It could look like this, however, this was still the exterior view of the preliminary design, i.e. changes will be made to the window on the west and east side.