Comparative offer roof pitch

Hello forum,
I have a question about the following situation. I ordered a city villa with a 30° roof pitch (hipped roof) without a converted attic. Due to a drawing error, it is now a 25° roof pitch. All documents + structural analysis specify 30°. Do you have any ideas on how to get more space volume in here? Would a comparison as a full attic conversion be okay for you? I am skeptical about that. I have already lost a lot of space in the roof due to the missing pitch.

We are talking about I assume (?)

Due to a drawing error, the roof pitch is now 25°. All documents + statics were specified with 30°.

I can hardly imagine the "drawing error" right now. So you ordered 30°, it was planned and approved as such, but the roof was built with a 25° pitch?
With 25° roof pitch, it takes 2.145 m to reach 1 m height, accordingly 4.29 m to reach 2 m standing height; with 30° pitch it would have been 1.73 / 3.46 m. You now effectively have 36.12 sqm at 10.30 m edge length in the area from 1 m height and 2.95 sqm floor area with 2 m standing height, compared to 46.78 / 11.42 sqm.
I understand your question / headline "Comparison offer" as you want to know what "compensation" would be reasonable (?)
Fictitiously calculated in 1 m high boxes (and without subtracting the hatch each time), you have 39.07 cbm storage space instead of 58.20 cbm, so you lose practically 19.13 cbm (mind you, based on a very rough back-of-the-envelope calculation). That would be about 60% of a single garage (using a comparable method). If the general contractor gives you a 3 x 3 m prefabricated garage workshop extension "for free," that would be, in my opinion, a fair compensation for both sides for the lost storage space. Alternatively: a single garage (manual swing gate, let's not overdo it) at workshop extension price. Of course, he also pays for the permit cure.

The drawing error came from the drafting office. 30° DN was written on it. But 25° was drawn. The statics, the building application, the contract, everything 30°. I don't know what such a roof expansion generally costs, mostly it is insulation wool and foil, a counter battens and rough plank sheathing applied. The issue makes me quite unhappy. Is a correction appropriate? Erect scaffolding, remove all roof tiles completely, take down solar collectors, replace rafters, and then re-roof.

Are 25 ° roof pitches even allowed? We have a hip roof with 25 °, and it serves as a storage room, but more than one room with slightly limited usability cannot be achieved with it.

If 30 ° were intended, I would not agree to this change, although I do not find a 30 ° roof pitch aesthetically pleasing on a tent roof.

Why has no one ever asked why the angles do not match? At the latest, the carpenter should have asked what applies now. In my opinion, the labeling takes precedence. Because I wouldn’t measure it either. Unless I have an advantage. Here, the carpenter has the advantage. You were probably deliberately not asked.

That is very annoying. If it was built differently than statically calculated and approved (both 30°), this must be corrected. Your damage in that case is a time delay. If only 25° was approved and then also built, there are several courses of action – which one I would choose myself I do not know immediately. Here it is important to gain clarity about your own goal. My goal would be to get the 30°. Another goal could be to receive the highest possible financial compensation. In the negotiation for the latter, I would prepare various calculation methods for the initial claim, e.g., what it would cost to redo the roof at 30 degrees, or how many square meters I lose and multiply that by the price per square meter of the house, or... In the argumentation, I would choose the one that results in the highest claim. There will be a negotiation anyway, so the starting point must be correct. Maybe your service provider has a good solution and nothing will be disputed. At least I wish that for you.