Cost estimate and final invoice

I also think these were net prices. Otherwise, how much is the difference in absolute price? €200, €20,000

I see it the same way as the OP. Unit prices were offered according to the bill of quantities. Most people here are probably not used to that, since they built with a general contractor. No fixed price but according to scope of work and quantity. Billing based on actual effort on the basis of the unit prices.

No one here knows the exact contract. Consult a lawyer.

The 19% strongly sound like forgotten VAT.

The engineer should explain himself as well. Just because the invoice amount is below the calculation, it is by no means correct.

The value-added tax was not forgotten. Offer amount 112,000 gross, after contract negotiation 134,000 gross, in the contract 137,000 gross. The offer as well as the renegotiations are part of the contract. Billing is based on measurement. Therefore, my simple consideration: position a from the LV + position b from the LV, all taken with the correct measurement. In the end, draw a line and add the agreed percentages from the contractual side agreements at this point. A 2% discount was granted. This does not appear anywhere on the invoice. I am not concerned here about being too expensive or too much, or anything like that. I am only concerned with the way the calculation is done. From the current invoice, it is not clear how the agreed percentages come into effect, because each position in the LV received a new price, sometimes more, sometimes less than 24%. But thanks to everyone first of all.

So 3,000 more. Since you are a community of owners, the 3,000 are divided among many. So rather a joke and not worth mentioning, in my opinion... Of course, you can discuss for weeks who calculated how, and think about suing... Or you just pay, and that's it.

So 3,000 more. Since you are a homeowners' association, the 3,000 is still divided among many. So rather a joke and not worth mentioning, in my opinion... Of course, one can discuss for weeks who calculated how, and think about suing... Or you just pay, and that's it.

Thank you for being so generous with our money.

Thank you for being so generous with our money.

What does the site manager say? Have you talked to the craftsman yet?