What can we finance?

Do you know anyone who builds like a rental apartment? That's technically not possible (keyword: utility room, heating, heat loss through exterior walls, own outdoor area and so on)

Currently less so. But there are certainly people who make sure that the installment including the service charge for a condominium does not exceed the current warm rent. Then there are those who base their financing including the installment on the current warm rent. The only problem is that in most cases (new construction) this leads to additional financing :-p

Then there are those who base their financing including installment on the current warm rent. The problem is that in most cases (new builds) this leads to additional financing

And after they have paid off after 40 years and paid 150k in interest, they sit in the house, pay for the third heating system, the second roof, and say that they have built a great retirement provision...

I can compare it relatively well in our case, as we have built quite close to the standard compared to many others here in the forum.

In 2014, we completed a small house with 125m² of living space, a 50m² steel garage, and the outdoor facilities on a 525m² plot. The whole thing cost around 300K€.
Equity 85K€
Loan 215K€
If you spread out the annual special repayments, we have a monthly rate of 1530€.
Remaining debt after 10 years 61,000€

If you roughly calculate what the house costs us over the 10 years, that would be
Equity 85K€
Installments 183.5K€
Reserves and non-allocable costs (estimated 250€/month) 30K€
=298,500

Against this stands the value of the house of 300K€ minus 61K€ remaining debt = 239K€

In this residential area, several houses of similar size, age, and equipment have already been listed with cold rents around 1200€/month online. That amounts to 144K€ rent over 10 years.

As tenants, you would have a surplus of 580€ between a rate of 1530 plus 250€ reserves and the cold rent of 1200€.
If you invest this together with the 85K€ equity, after 10 years at a 4% return you would have 212K€, at 5% 230K€, and at 6% 250K€.

Assuming the house is not worth less (which is unlikely given the increase in land prices from 80€ to 200€/m²), we would have had to achieve a 5-6% after-tax return with the capital.

Rent increases would further improve the result in our favor.
A consideration period >15 years would also have a positive effect in favor of ownership due to the elimination of the installment.

For us, it was definitely worth it, assuming that we as tenants would also have chosen a house.
This may look quite different in other regions, with different repayment rates or at different times.

I can compare relatively well in our case, as compared to many others here in the forum, we built quite close to the standard.

In 2014, we completed a small house with 125m² of living space, a 50m² steel garage, and the outdoor facilities on a 525m² plot. All this for around €300K.
Equity €85K
Loan €215K
If you distribute the annual extra repayments, we have a monthly rate of €1530.
Remaining debt after 10 years €61,000

Roughly calculating what the house costs us over 10 years, that would be
Equity €85K
Installments €183.5K
Reserves and non-allocable costs (estimated €250/month) €30K
= €298,500

In contrast, the value of the house at €300K less €61K remaining debt = €239K

In this residential area, several houses of similar size, age, and equipment have already been listed for cold rents of around €1200/month online. That amounts to €144K rent over 10 years.

As a tenant, you would have a surplus of €580 between the rate of €1530 plus €250 reserves and the cold rent of €1200.
If you invest this together with the €85K equity, after 10 years at 4% return you would have €212K, at 5% €230K, and at 6% €250K.

Assuming the house is not worth less (which is unlikely given the increase in land prices from €80 to €200/m²), we would have had to achieve an after-tax return of 5-6% with the capital.

Rent increases would further improve the result in our favor.
A consideration period >15 years would also favor ownership due to the elimination of the installment payments.

For us, it definitely paid off, assuming that as tenants we would also have decided on a house.
This may look very different in other regions, with other repayment rates, or at other times.

And how much money do you invest in your house within 15 years? And in the garden where you always want to make something nice or different?

It’s already late and maybe I’m making a mistake, but if you spend 299k within 10 years for a value of 239k, you’ve initially lost 60k.
However, you have saved 144k in rent during the same period, which means you would be 84k in the plus.

Now you could have alternatively invested 85k as a lump sum and another 580€ monthly, and with just 1% interest on the capital (taxes probably wouldn’t apply to a married couple at these amounts), I already come to a sum of 167k that you missed out on.
So you have spent at least 83k for the luxury of owning your own home, haven’t you?!

and how much money do you put into your house within 15 years? and into the garden where you always want to make something nice or different?

Planting, etc., you would also do as a tenant if you plan to live there long-term. You are surely right that as a homeowner you will invest more than a tenant.