Additional cost due to tile size?

Thank you very much for your opinions. We had a lot of trouble with the developer in the past few months. The site manager has been sick since the beginning of the work, and the new site manager is unfortunately a bit uncooperative. Then it often comes up like "do you have that in writing?" which was actually fixed in writing sometimes, but sometimes only discussed verbally with the "old" site manager. Result: we had to pay €700 for two small walls in the bathroom that should actually have been included in the price... well. That is why we are also making sure that we get our "rights" according to the contract (just like the housing association). By the way, the developer is now paying the additional cost....

By the way, the developer is now paying the surcharge ....

at least something ... besides all the trouble!

If a pure material price was agreed upon, it is legally a problem for the BU. We had ordered in the contract for work 70.00 euros/sqm and 120x60 cm porcelain stoneware for 69.50/sqm. As expected, there was an additional price agreement, which we rejected with the help of the [Bauherschutzbund] (as many before). The BUs simply try to pass all costs on due to their own calculation errors, and far too many building owners play along due to their own inexperience.