Construction cost payment schedules

The guarantee also applies to the services included in the [Bauleistungsbeschreibung].

However, during construction, there are so many things that are not included or that one wants additionally that quite a sum adds up.
- Tiles (additional cost for higher-quality tiles/for type of installation/for tile size/edge finish/additional sealing measures, etc.),
- Sanitary (any deviation from the standard I find really expensive here including bathroom furniture - shower enclosures, for example, were not included in any [Bauleistungsbeschreibung] I have read),
- Electrical (number of sockets/LAN),
- Additional burglary protection for windows + doors,
- Lightning conductor,
- Snow guards
- Roller shutters (manual/electric)
- Underfloor heating
etc.

Yeah, that's probably true, but is it often the case that you have to top up such an amount? The developers do advertise a fixed price guarantee a lot.

One does not exclude the other.
With the GÜ (general contractor contract), the house has a fixed price, but then the soil report requires higher reinforcement, better statics, more complex earthworks. That's when the buffer you set aside for the fittings can come into play.
We naively estimated 500 for the carport... but of course we didn’t want a DIY store carport, but an aluminum carport including professional foundations, which are never factored in.
Spontaneously, during the construction phase you want a second outdoor faucet, the garage then with electricity, the tiles done by yourself turn out to be more expensive, and no one said that glue is expensive ;)
You can’t get the outdoor lighting for 10 €, and now you want eight in a row on both sides because you planned it nicely, but without bulbs. The satellite system also doesn’t appear in any construction service description... and so on and so forth...

Or do you know how expensive a mailbox is? :)

... and the often neglected rainwater drainage, with our cistern it cost another 5000 :(

I believe it never hurts to have around 10% of the construction costs lying around somewhere (or to know that the bank would refinance such an amount).

And I have never seen a construction project that was calculated sufficiently from the start including all extra wishes. Not one!

Either the bank helped out or the own reserves.

Either invest your own effort or simply forgo something - or negotiate with the craftsmen. These options still exist - foregoing is the easiest and at the same time the hardest :D