Costs are rising sharply - is additional financing currently possible?

What do you mean by started building? Earthworks, foundation slab, or even the shell construction? If you do individual contracts, you can still control a lot. Concrete or even metal instead of clay roof tiles, EPS instead of mineral wool (although I don't even know if it is really cheaper at the moment, this is just an example), gypsum plaster instead of lime-cement or clay plaster, attic instead of rafter insulation, plastic windows instead of aluminum, laminate instead of parquet, dispersion paint instead of silicate paint, laminate instead of parquet, leaving individual rooms that are not needed completely bare for now (no electrical fittings either, just pulling cables). And then do more own work. Installing windows, chiseling grooves, pulling cables, insulating the ceiling, drywall. But be careful, that also takes its toll.

As a short calculation example for this (and possibly other) consideration(s): €200/month is €2,400/year, which would correspond to 4% interest (without repayment!) on a loan amount of €60k (2400/60000 * 100%). That means: with interest >4%, €200/month is not even enough to cover the interest costs, let alone repay the additional loan.

You can increase your monthly burden up to €1650 (interest and repayment) I also do not consider the price range realistic, please immediately remove at least the garage Otherwise, you and the neighbors will notice the financing problem at the latest when you cannot afford exterior plaster.

Are the mandatory 20-25% buffers already included in the calculation of the 650k? That would at least cushion some price increases and unforeseen/forgotten items. With 650k and EL, you can already build a lot... it usually gets tight towards the end.

With 650k and EL you can already build a lot.... it usually gets tight towards the end

Yes, but not with the described EL, rather if you really put in the hard work yourself.

Did you calculate that yourselves? Or is there an architect who also awards the contracts? Somehow it seems a bit half-baked to me and you are building too big a house? Couldn't the architect have planned that more efficiently?

did you calculate that yourselves? Or is there an architect who also awards the contracts? Somehow it seems a bit unrefined to me and you are building too big a house? Couldn't the architect plan it more efficiently?

If you have two useless rooms upstairs, any architect involvement would surprise me...