House construction project - Reality check

Hello,

I would need an assessment of my project.

About me:
M33, single
Work in IT (insurance), 38h/week
3.8k net, 14 salaries, tariff
Equity capital: 50k (there is additionally a reserve of ~40k / stocks)

Current fixed monthly expenses:
671€ cold rent + 150€ additional costs + 40€ parking space
Electricity: 46€
Internet: 35€
Insurances: 123€ (liability, household contents, car)
Car fueling: 100€ (electric new car from the end of 2023)
Public transport ticket: 29.9€
Mobile contract: 12€
GEZ: 18.36€
Living expenses: 500€ (including eating out, etc.)
150€ other reserves (electronic devices, general apartment, sports club, …)
------
1876.26€/monthly

Monthly savings rate: 1500€ - annual savings rate is higher as lump sums are mostly set aside. Realistic currently: 25k€+/year

My wish would be to build / have built my own property. Preferably off the shelf with little personal contribution. Possible own contribution would be laying the flooring and wallpapering.
House size ~120sqm
Price per sqm new development area fully developed: 150€/sqm – Lower Saxony – Heidekreis. Building plots are usually 650sqm+
So far I am calculating the following:
Plot: 100-110k
House: 360k (catalog price e.g. Viebrockhaus or roughly 3k€/sqm)
Outdoor facilities + ancillary costs: 50k

Certainly something is still missing in the calculation (kitchen for example). And to round it off, I would approach a total cost of 550k. Roughly speaking, about 500k to be financed. The wish (or pipe dream?) would be to pay everything off in under 30 years, including a planned annual special repayment of ~5000€. I would set the installment at ~2k €.

And now the question to the group is whether this is realistic. Are there experiences with similar parameters? What does the practitioner from the bank say? Better to let it go and look for a somewhat cheaper, young, used house? Especially considering that I am far from the rough guideline like “maximum 35% of net income.”

So, roughly 500k would be eligible for borrowing.

With an average net income of €4,400 and a monthly payment of €2,500, a bank will say "No". Why a payment of €2,500? That is an annuity of 6%, so that you are done in 30 years. It could also be higher, since you basically need full financing.

You are the perfect candidate for a used property that can be resold repeatedly without loss. So reasonable location, reasonable layout, and not too worn out.

I would like to point out a few things in your cost breakdown. The car is currently new. What will you do in 8 years? Either you build up reserves (the specified €150 is already allocated for many other things) for a purchase or there will be another monthly expense like leasing or financing. €500 per month for living expenses. So food at work (canteen?), at home and out, clothes and hygiene? Respect. With €12 mobile phone costs, certainly no smartphone is factored in, that should then be included in the reserves or living expenses? If not, an iPhone 11 still costs a good €500 (spread over 24 months that is €20.83/month). In the single-family house, the ancillary costs increase approximately linearly with the living area plus the usual maintenance costs for the property / outdoor facilities. The same applies to the reserves. If a radiator breaks in the rented apartment, the landlord steps in. In the single-family house, such failures are "your problem." You earn good money, but as the sole earner, I cannot imagine that the bank will lend you this amount for a new build. So much can happen before the building is finally completed, and the banks know that too. I think the default risk is too high here. The difference between the property value and the loan is too small.

One could also calculate differently:
Average living expenses in Germany are around €1800.
Cheaper Heidekreis possibly at €1500?
You still have €2300 left from €3800. Two months' salary for your special repayment, reserves, and vacation not included.
From €2300 let's subtract a modest €300 for additional costs = €2000

House €360,000 + land €110,000 + outdoor facilities/parking space/carport €30,000 + incidental construction costs €30,000 + other €20,000 - equity €50,000
= €500,000 requirement

A few online calculators say that the ratio doesn't add up.

I would ask why even have a house as a single person. I would buy a nice apartment and if a wife and child do come, then sell it and build a house.

(...)
In a detached house, the additional costs increase approximately linearly with the living area, plus the usual maintenance costs for the property / outdoor facilities. The same applies to the reserves. If a radiator breaks down in an apartment, the landlord steps in. In a detached house, such failures are "your problem."
(...)

No.
Only the heating costs increase somewhat linearly. Electricity and waste fees depend on "consumption," not on the living area. Insurance also doesn't increase linearly with the m² because the greatest risk is initially the property itself. Whether it is 100 or 200m² raises the amount of damage... but not the risk of a damage occurring.
Also, the maintenance of the property, possibly street cleaning, property tax... all only relate marginally to the living area of the house.

This is the case with all insurances, including car insurance. Whether I drive 5,000 km or 50,000 km doesn't really make much difference in the end.