Unpredictability of construction costs - Will the project fail because of it?

Let's get back to the question. I would not build the house like that and due to the unpredictability of construction costs would reconsider the plan thoroughly. You do not have any viable offers yet, except for the shell construction, which for inexplicable reasons has already become more expensive today.

True enough. I just spoke with legal advice and the construction company. Legal advice says that the offer was a binding contract that must be honored and prices should no longer be adjusted. The construction company says that the offer was not yet a complete contract and they can prove the price increase for steel and co. With the friendly note that if we insist on the old prices, they would probably have to postpone the construction project indefinitely…

But he also overlooked the ceiling height. By the way, I'm really keeping my fingers crossed for you! Focus on what said!

Unfortunately, that's also true again..

AB: storage room.
Washing machine connection is missing... fitting kitchen, bedroom plus living room into 17 sqm and then selling it to the authorities as a granny flat is bold.

But whatever: why should we care how this happened. Now it's about how to make an affordable house out of it!
So focus on that!

A granny flat with a ceiling height of 2.25 m is not habitable anyway. Why doesn't the building authority see such a defect?

We see the necessity for redesign. The OP sees it differently.

True enough. I just spoke with a legal advisor and the construction company.

The legal advisor says that the offer was a binding contract that must be honored and the prices should no longer be adjusted.

The construction company says that the offer was not yet a complete contract and they can prove the price increase for steel and co. With the friendly note that if we insist on the old prices, they will probably have to postpone the construction project indefinitely…

These two statements could have been made by me as well. It was to be expected after the construction company talked you into a basement.

An apartment with a ceiling height of 2.25 m is not habitable anyway. Why doesn’t the building authority see such a defect?

We see the necessity of replanning. The OP sees it differently.

It’s not that I categorically rule it out. I just don’t know right now how that’s supposed to work! Stay with the old construction company or try to find a new one? What about the loan if we replan the property and omit the basement? Those are questions I can’t answer immediately!

How is he supposed to just simply reschedule the whole thing? Is everything really that easy? Seriously asking, I don’t know how that could just work like that? The loan is running and whether the bank would go along with a changed property without any issues, I would just doubt. Possibly a new loan with completely changed interest + early repayment penalty for the current loan? Additional costs for rescheduling with the general contractor? Possibly months of processing time and continuously rising costs during that time? Additional costs for a new building application and new building permit? Is the whole rescheduling still "economical"?