Single-family house + granny flat on a slope with flexible use

The housing market is currently good for landlords

That's nonsense, considering the construction costs. Rents have risen a bit, yes, but construction costs have exploded! Take your current rent and try to pay off the m² x 2000 for it. How long are you paying? After 15 to 20 years, you have to renovate everything, and with a granny flat, the turnover can be much higher because it is often only used temporarily – meaning it wears out faster. And 2000 is already rather a lower-end standard.

Anyway, if you prefer to sit on the balcony, that's each to their own. I see the budget much more as a limitation to 2 floors, and then it gets reshuffled and reconsidered anyway.

how often children are in the garden in our latitudes?
About 330 days and on about 150 days a year you can't get them inside the house
At least the Bavarian country child

No, it's not logical that the house with access from below has the living area downstairs.

My parents have a plot with access from below and live on the upper floor because the south-facing garden is there. Everything is one stair up and that is good and practical

That’s nonsense, considering the construction costs. Rents have gone up a bit, yes, but construction costs have exploded! Take your current rent and try to pay off the m² x 2000 for it. How long are you paying? After 15 to 20 years, you have to renovate everything, and with a granny flat the turnover is possibly much higher, since it is often only used temporarily – meaning it wears out faster. And 2000 is rather on the lower end of the quality range.

Anyway, if you’d rather sit on the balcony, that’s everyone’s own thing. I see the budget much more as a limitation to 2 floors and then everything gets mixed up and reconsidered again.

You forget that the granny flat is not built bigger separately, but only the use of currently unused rooms is changed.

I actually didn’t want to reply to the last post from the OP here, since much contradicts itself and apparently several strangers or postmen get more weight per day than life in the garden, i.e., the switch from a cooking pot to a shrub.
It is also confusing that arguments against a voyeur window were requested, now no longer.

Therefore, roughly speaking: you mustn’t lie to yourself, affording something even though you cannot afford it. That can backfire quickly. Apartments where the owner lives in the building themselves, I don’t even find appealing on vacation, because they always nag whether you behave “properly.”
That significantly reduces the target group, if one has even thought about it at all. Over 40sqm all-purpose room with tiny bathroom and bedroom... it will be a single person. But they don’t like strange children in the house, etc....
Besides, rented spaces are worn out after 10 years, then expensive remodeling...

I would only tackle this house with a good architect who knows to what extent the load-bearing basement walls can even be opened for doors. Certainly doable, but construction costs will be higher, remodeling costs, renovations, and if the government regularly wants its cut, in the end not much is left except a stranger’s car in your own carport, which doesn’t fit.

You forget that the granny flat is not built larger separately, but only the use of currently unused rooms is changed.

No, I am only explicitly referring to the previous quote, "the market would be great for landlords." They actually have to constantly maintain the worn-out building, and that is currently more expensive than the rents bring in. This also applies to the granny flat.

Of course, the income temporarily makes the 3 children's rooms seem like a cheap acquisition, but as soon as the children are supposed to move in, a renovation + conversion will be necessary. That can become painfully expensive. Taxes also still have to be deducted from the income. In addition, the investments for the outdoor facilities will probably be more expensive due to separate access than without a granny flat. What is left then?
All that hassle and the constant proximity of a stranger in my house – never!

I lived for a while in the two-family house, upper floor/attic, with another apartment below.

The terrace in the garden was usually too far, we only moved everything out in exceptional cases. The ordeal of quickly going into the house to get something you forgot beforehand, with a small child (whom I couldn’t leave alone because of the pond)... Even though that phase passes, I have unpleasant memories of it. Of course, I was with the kids in the garden, but that was kind of a separate activity, like going to the playground.

The lower apartment (ground floor) belonged to the father of my ex. Since he passed away, it has been vacant. We already considered back then, what to do? Permanently bring strangers into the house? Shared flat with two student rooms, preferably for students who go home on weekends? Vacation rental, then at least you don’t have someone there permanently yet still have some income from time to time? My ex’s current solution: in a city where apartments are actually very scarce and in demand, the lower floor simply remains empty.

Does anyone possibly have ideas for the layout of the rooms in the basement?

Also take a look at (there we had the reverse topic, being able to convert the children’s rooms later into a granny flat), or also – aside from the fact that we mostly don’t see it aiming for a hard landing there – at – and basically imagine all examples you can find in forums the other way around as well (i.e., take a split-level upper floor also as an example for one half of a basement).

Once again, fundamentally about granny flats: 1. such is never really economical if it starts with increasing the budget; 2. this applies even more severely to plots on a slope. Besides, I wouldn’t call myself a "smoker" with my half dozen cigarettes a year. The same roughly applies to a "landlord" of a single granny flat. You will never, ever – that is in no market situation! – become a “landlord” in the sense of a serious source of income with a single housing unit.