Planned for months and now additional costs because it is not feasible?!

Hello everyone,

I have a small problem: I planned the house with 4 folding systems, all of which can be pushed outward.
2x 4.30 m wide
2x 3.30 m wide

It has been planned for half a year that the large folding systems have 4 elements and the small ones only 3, so that each element is about 1.10 m wide and it looks uniform. Also, roller shutters because they provide the best darkening.

Now, right before ordering the windows, the builder comes with the following statements:
1. For the two 4.30 m folding systems, the window maker cannot offer insulated roller shutters, as they would otherwise sag.
2. The 4.30 m folding systems are only available with 5 elements.

Regarding 1) His suggestion: I should switch to venetian blinds because they are apparently available in that width. However, with an extra cost that he has not told me until today.
Regarding 2) His suggestion: I should rather take a PSK door, which is also cheaper... or I should add one more element to the small folding systems as well so that it looks uniform. Another option would be to have the folding systems made of aluminum. That would achieve the dimensions. However, here again nearly €4,000 extra cost.

Now my questions:
Who has to cover the additional costs for venetian blinds and aluminum folding systems?
A builder with a draftsman and architect should know whether roller shutters are available in such widths and whether folding systems with a certain number of elements are deliverable or not.

If I had known the additional costs beforehand, I would certainly have reconsidered, but the shell is built and re-planning now is difficult.

Best regards
Tito

What was agreed? What is stated in the construction description? What exactly does "was planned" mean? Were the "folding systems" sold to you as described by you with these properties? If yes, they must now be delivered. If no ...

Is it really a developer or is it a general contractor or a construction manager?

What was agreed upon? What does the construction description say? What exactly does "was planned" mean? Were the "folding systems" sold to you as you described with these properties? If yes, then they must be delivered now. If no ...

Is it really a property developer or is it a general contractor (GU) or a main contractor (GÜ)?

Hmm, so the construction description only mentions plastic folding systems and nothing about the division of the elements. But it is shown that way in the construction plan, it was also marked that way from the beginning in every version of the construction plan.
Regarding the shutters, the construction description states: electric shutters in every room.

The contract states that the following documents apply to the scope of services:
- Offer including construction description: The issue of shutters is clarified here. There is no exact information about the folding systems.
- Construction sketch: Here shutters are marked with "Ro", also at the folding systems. The folding systems themselves are drawn here with the desired 4 elements at the large openings and 3 elements at the small openings.
- Room book: Neither of the topics is mentioned here.

If I read it like this, then he should bear both additional costs, correct?

What is a GU or GÜ?

Regards
Tito