Did you all overlook that? How is that supposed to work?
Well, it's quite tight but depending on where he wants to build, how much personal contribution he wants to put in, which trades he can get cheaper through connections, and how much he holds back on the equipment, it's definitely possible.
In the end, we come to 165 sqm and with everything, we're well below the common 2000€/sqm + incidental building costs here. Affordable building area, organizing trades oneself, a lot of personal contribution, and a bit of connections make it possible.