There is usually at least a factor of 2 between a company's offer and the material price,
there are reasons for that. Labor time and not to forget equipment have their justified posts, which of course are reflected in an invoice. Every entrepreneur has to proportionally calculate his acquisitions and wages into his invoices, otherwise he would never be able to pay for his equipment or craftsmen.
Without going into all the details: If you roughly estimate the whole thing, you arrive at a manageable budget,
I do not see it that way. Of course, own work relaxes the financial situation, but from a flat assumed €830,000 (200 sqm living space x €3000 + 100 sqm basement x €1500 + €50,000 incidental construction costs + €30,000 garage) you do not make €500,000.
where for the respective trades only the material costs are charged and, of course, your own time ;-)
That is not correct: as a rule of thumb, you can add another 1/3 to the material costs for work equipment and small items. (At least that always worked very well for us)
And even if you want to take 2 years, you have not made the invoices with your body, which will eventually be mentally and physically worn out.
I assume that you are still working? and also want to work 8 hours/day? Apart from the driving around to the construction site and hardware stores to get equipment/small materials, you are left with only about 20/25 hours a week that you can bill at €20/hour. As a layman you will need double the time anyway compared to a trained craftsman, your friend and helper might possibly sacrifice his private time for you for 2 weeks, but not for a year, and certainly not unpaid.
To clarify once again: you work at an hourly rate worth €20. That is 25 hours per week, so €500, per month that's €2000.
That is roughly €20,000 in 10 months. For €200,000 you therefore need 100 months.
For painting work, floor coverings and the like, also the odd small task, you roughly consume your annual vacation.
And then there is the dear boss, who looks the other way for a while, but not for a year, where his employee focuses more on his construction site and on YouTube videos about DIY work than on recovering and recharging energy during weekends/vacations for his earnings.
Regarding rough estimation and own work: the bank wants figures that are comprehensible and where the own work is also feasible within a framework. Also within a time frame. They will finance a "turnkey" house more than a long-term construction site where you limit your craft knowledge to painting work and garden landscaping.
In my cost calculation, such items only appear, among others, for the house connection, excavation, compaction, windows, roof truss, stair covering and roofing. The rest is done by own work or together with friends,
I find that somewhat "uncoordinated": you could actually do the excavation yourself, also the stair covering, and the roofing should not be a big deal either.
Regarding the floor plans: no discussion with only one floor. That usually does not work. Basically, they can all reduce the living area a bit, whether the house is executed in EL or by a specialist. Anyone who has €500,000 available does not reach for the stars. That’s my opinion.