Only the finished ground floor would initially be about 80 m2, if you plan the upper floor as expansion potential. If I calculate 2000€ per m2 of living space due to the unfinished upper floor (which still causes costs), I end up with 2000€ times 80 at 160,000€, with incidental construction costs about 180,000€. I can finance that.
Maybe this will help you. I am currently building a two-family house together with my brother with (at least for this forum) an extremely high amount of own labor. Before Christmas, the screed will be installed. Once the screed is in, we are at about 1350€ per m2. The living space is 250 sqm because there are two apartments, but also more installation needed. Of course, there is only one roof, foundation slab, etc.
Own labor:
-Roofing, roof insulation, vapor barrier and later also attic ceiling and knee wall with drywall
-Electrical work completely
-Earthworks
-Roller shutter installation
-Insulation under screed
-Horizontal sealing of the foundation slab
-Garage (I had one left over) self-assembled
-Wood substructures for tinsmith work (loggia roof)
-Countless preparatory works for the trades
The incidental construction costs come on top with 160€ per m2.
So we are now already over 1500€ per m2 including incidental construction costs with above-average (for this forum) own labor.