That’s why I also asked for a rule of thumb following the scheme:
"How much does the material cost in a shell construction for about 200,000 euros?"
If it were 100,000 euros, I could estimate:
100,000 euros are bricklayer’s own capital + 25% surcharge + 19% VAT, so I would pay xx.xxx euros less for the same material.
I have to start somewhere and at least partially eliminate some unknowns.
Hence the assumptions above of 600,000 euros for a standard detached house with about 150 sqm turnkey in price-performance winner execution, so without golden faucets, but they can be from (Hans) Grohe.
Plus the statement of the building materials market manager, as an assumption, that it already works with the material and if the craftsman demands a "handling fee," then that can be discussed. For that, he doesn’t have to pay invoices, has less bookkeeping effort and no tied-up capital.
And X0,000 euros savings through cheaper material, help from the brother-in-law, and EL vs. turnkey building can definitely tip the scales clearly towards the east.
Under these conditions, I estimate you could save XXXX€ - XXXXX€.
Seriously: don’t you realize yourself that this won’t work and is just poking around in the dark?
-> Go to the bank and have them calculate the credit limit based on your income. Then have the mother’s girlfriend draw a first floor plan and get one or two offers. On that occasion, you can also discuss the material procurement story.
With your XXX€ savings at XXX% discount and XXX€ craftsman surcharges, no one can give you any sensible advice.