How should I plan to afford this?

And are you already building or do you have a fixed price?

We already have the plot and are building with 350,000 EUR solidly with a usable basement and 140 sqm living space (excluding basement). The 350,000 EUR includes additional construction costs as well as kitchen and inventory and also some nice extras and all this also in Bavaria

ok...with 140 sqm probably doable. But 140 sqm is rather small. At least where building land is very expensive. For us it's about 200 sqm and that marks the lower end.. The average here in our settlement (high land prices) is probably >250 sqm... quite crazy all.

@ Lexmaul: Fixed price
I just wanted to show with my statement that you can’t get a house with a granny flat and a basement for 300K EUR... unfortunately

ok...at 140sqm probably doable. But 140sqm is rather small anyway. At least where building land is very expensive. For us, it’s about 200sqm and we mark the lower end... The average here in our settlement (high land prices) is probably >250sqm... pretty crazy all around.

And we hardly dare to mention our 154sqm here, because the neighbors all build with 100-120sqm... But the reason why high land prices also mean high sqm numbers doesn’t quite make sense to me.

Presumably because expensive plots attract high-income builders? There are no plots under 280,000 EUR (>1000sqm) here, and usually houses worth 200,000 EUR are not built on them, but rather more in the 500,000+ range. We are rather the exception... simply because we fell in love with the location.

And we hardly dare to mention our 154sqm here because everyone in the neighborhood is building with 100-120sqm

Why, you can be proud of what you have achieved.

Just because the average in East Germany is around 130 sqm (as of 2012) there are still outliers both above and below.