Own contributions? What is feasible?

Interest rates are below 3%, 10,000 EUR special repayment per year, free construction account, etc.
My house is calculated by the architect based on a certain construction sum. The bank goes by this construction sum. Minus equity, own contribution, etc. If I do not state as much own contribution as I probably will provide and, through the tenders and negotiations with the companies, some things turn out cheaper than calculated, then in the end some money will be left over. This is better than if I calculate everything down to the cent and then have to refinance at the end.
I decide how much loan I need and want to take out!!

Interest rates are below 3%, 10,000 EUR special repayment / year, free construction account, etc.

My house is calculated by the architect based on a specific construction sum. The bank goes by this construction sum. Minus equity, own work, etc. If I now do not specify quite as much own work as I probably perform and through the tenders and negotiations with the companies some things become cheaper than calculated, then money remains at the end. This is better, isn't it, than if I calculate everything to the cent exactly and have to refinance in the end.

I decide how much loan I need and want to take out!!

What term do you have? 5 years?

You decide how much money you want, the bank either gives it or says NO.

Even architects can base their calculations on wrong numbers. Just happened to the neighbor. Five-figure sum just for the plumbing trade.