Hello Matthias,
the financing could look like this for you:
72,000 EUR KFW 124, 3.65% / 3.70%, 10 years fixed, 100% disbursed, repayment: 1.50% from the 2nd year = 309.00 EUR monthly.
42,000 EUR construction loan, 3.75% / 3.82%, 10 years fixed, 100% disbursed, repayment 1.00% = 166.25 EUR monthly.
96,000 EUR own work = 40% of the total construction costs
30,000 EUR equity
240,000 EUR total (mixed interest rate: 3.74% effective) = 475.25 EUR monthly.
On my homepage you will find in the "Infothek" in the area "Download Forms" a template "Baukostenzusammenstellung" which can help you with the more precise planning of your total costs and your own work. Please download it.
Best regards
M. Thiemann