Gypsum board ceiling hangs lower than expected - What to do?

Would you say from the architectural plan I attached that the clear room height is 250cm? Or are those the 250cm up to the beams (which is true)? Unfortunately, it is not clear. Now one might think it is the beams, but as a layperson, one thinks it is the finished ceiling.

I would also read the plan as "250 to the bottom edge of the beam." But something must have been communicated about this beforehand, right?! After all, the suspended ceiling is not shown in the plan either.

The construction of about 6cm is common. GK board + CD profile is about 4cm and then there are about 2 cm left for height adjustment because the beams are also not perfectly level.

Apparently, two counter battens were installed underneath to make it more stable than just one. Possibly one would have been enough, but the drywall builder decided on two.

But the trouble continues: the tiler has now tiled the tiles up to the ceiling (100% horizontal according to the spirit level) and it is now noticeable that the ceiling is crooked. That means a deviation of about 1-2 cm over a tile length of 90 cm. Normally, this is not noticeable, but now you can clearly see the widening gap between the ceiling and the tile.

Are such sloppy works normal? What can be done? Can the ceiling be corrected, or does the painter have to even it out later with filler work (but then the ceiling will be even lower :-/).

Cornice above.

There are, as everywhere, certain tolerances that one has to live with. I would feel inclined to say that 1-2 cm over 90 cm exceeds this limit, but you should ask a professional about that.

Personally, I would probably be annoyed as well, not least because nowadays, thanks to appropriate tools (laser) and more dimensionally stable materials, it should actually be possible without any problem to execute such a suspended ceiling accurately.

Nonetheless, of course, one should weigh whether one could live with a makeshift solution like the (stucco) moldings suggested by Nordlys. That can look very good on its own, saves you from having to close the gap with acrylic or the like, and in the end, you also have to realize that even a "code-compliant" execution will never be as perfect as some mechanical engineers at construction imagine ;-)

I would probably suggest to the drywall installer to correct this optionally or to install appropriate moldings at his own expense. In any case, you won’t be able to compensate for this with filler...