How do you assess the financing options?

Hello everyone,

Our construction project is currently becoming more concrete, and therefore I would like to hear your opinion on our financial situation and the "leeway" for the construction to compare it with my assessment.
Here is a brief overview of the current state, which is very accurate due to the household budget:

He (28)
-Industrial Engineer M.Sc.
-permanently employed in a management position
-€3,200 net per month with 14.5 monthly salaries ([Steuererklärungsklasse IV]). Salary will increase to €3,400 net per month in one year.

She (26)
-Nursing manager
-permanently employed in a management position
-€2,300 net per month with 13 monthly salaries ([Steuererklärungsklasse IV]). Further salary increase currently not foreseeable.

Family situation
-married, no children yet (but one or two planned)

Financial situation
-fixed savings contribution from both €2,000 per month (excluding special payments like 13th monthly salary)
-monthly expenses for private retirement provision €450 per month (could be temporarily reduced by €250)
-current cold rent €750 (warm: €1,025)
-other expenses for insurance, car, further savings for vacations, etc.

Equity
-immediately available: €65,000
-capital in allocation-ready building savings contract: €25,000 (would give a loan of approx. €35,000 at 3.07%)

Construction project
-approx. 600-650 sqm plot at a price of approx. €150/sqm
-Frisian house with approx. 150 sqm living space with own work (floor coverings, tiling work, installation of bathroom fittings, ...) Before the question arises: Yes, we trust ourselves to do this and have the skills :)

Financing framework
-even though a house is very important to us, we do not want to start the project if we have to cut back everything else for it. Therefore, we thought of a monthly burden of approx. €1,500 - €1,750 (max!), to save money besides the financing.

How do you see our possibilities? What can we afford and where are our limits?

If you need further information, just let me know briefly.

Thank you very much!

I wouldn't consider taking advantage of the [Bausparvertrag] :D
1750 / 0.055 -> 380 k€ - 150*650 sqm = 282 k€ + 65 k€ -> 347 k€ - 50 k€ additional construction costs -> 297 k€ / 150 sqm = 1980 €/m² ... should be enough.
If you both work in Hamburg, you might want to consider building closer to the city.

I need to make a small adjustment: The building savings contract has an interest rate of 2.00% and not 3.07% as shown above. , thanks for your calculation, but you have completely neglected the saved €25,000 of the building savings contract?! And since we both work on the border to SH or already in SH, a house outside of Hamburg makes sense. What I forgot to mention: We would like to build with a basement, if financially and soil-technically possible.

Now I am slightly overwhelmed... I believe basement space costs 1000 € per sqm (?) - so another 75 K€ on top. House 1600 €/m² -> 240,000 € (house) + 75 K€ (basement) + 50 K€ (ancillary construction costs) + 110 K€ (land including purchase incidental costs) -> 475 K€ for everything, compared to your 380 K€ + 65 K€ + 25 K€ -> 470 K€.
So it still fits.

Oh man, those are prices.... who is supposed to pay that

Oh man das sind Preise....wer soll das bloß bezahlen

It can be done much cheaper: - smaller plot 400 sqm is also enough - no basement - somewhat less living space etc.