€10,000 are for us just 'property-specific work', connections from municipal utilities, telecom, and wastewater / rainwater pipes. Then there are additional electrical wishes (€3,000 if you are modest, but it can quickly become €10,000), notary, taxes (depending on your place of residence and property), and an estimated €5,000 over the entire construction process for surveyors and fees for land register entries.
So far, we haven't included paving work for the house path, terrace, parking space, no garage, no splash protection around the house, no lawn, no fence, no kitchen.
Make two lists for yourselves:
one with all expenses per month, and don’t forget annual ones like car tax. Also include a savings amount for a broken washing machine, car, and vacation.
another list with all additional costs, e.g. based on this list:
It's nice if you think you can get by with less, but the craftsmen will teach you otherwise. Except for the electrical work, we had no choice whether to accept the offer or not – the house simply needs electricity and wastewater. And many things we are only doing later. It's best to have a 10% buffer on the entire calculation for unforeseen disasters or special requests (after all, you only build once....) And it’s the many small amounts you didn’t know or ignored because they seemed so small – but here €500, there €500 can easily break your back or at least lead to a more expensive additional financing.