Hello everyone,
we are currently also building a single-family house in post-and-beam construction including a basement (masonry). In total, spread over 3 floors, it's about 230 sqm, which would cost us around 345,000 euros without own contributions – so about 1,500 euros per sqm. Fortunately, we had an excellent architect who really (hopefully) showed us all additional costs in advance and set them very generously. Essentially, these were (of course, this is always a case-by-case basis!):
1. Earthworks with sufficient gravel and drainage... = 20,000 euros
2. Outdoor facilities = 15,000 euros
3. Garage = 10,000 euros
4. Construction electricity and water = 2,000 euros
5. Connection work (water, electricity, telecom) = 3,000 euros
6. Notary = 1,200 euros
7. Approval procedures = 1,000 euros
8. Possibly structural engineer, surveyor, geometer = 2,000 euros
9. Buffer for these items = 5,000 euros
About the earthworks: For us, it was natural soil and excellent humus! Could not be better, no rocks or similar. But a small water vein and a bit more rolling gravel already add a few thousand euros...
Then come all the extra wishes like additional sockets, lamp outlets, window frames in a different color, stairs in a different type of wood, higher doors, different sanitary installations, etc. I would have ALL of that put in writing in advance (e.g. extra cost per socket, etc.). I would also look at the subcontractors, have the goods shown and negotiate surcharges with them. I think often it is already the case that prices are pressed quite hard with the standard and then a lot of money is made on special requests, also on the part of the subcontractors. And especially when there was no clear offer in advance. So very important: Be clear about additional construction costs and special requests!