Floor plan design single-family house in L-shape

The area with the sofa looks like a waiting room, an absolute thoroughfare. In my opinion, that just doesn't work.

Oh, yes, through the "living room" – here more like a hallway with a sofa – to the toilet. Moreover, in these two floor plan variants, traffic areas are only created by this, while actually hallways are supposed to be avoided.

Regarding the basement: if the basement becomes a full storey, it might be that it can no longer be built as is -> BePlan.

In DE, fully underground full storeys are irrelevant, but you probably don't need to worry about building regulations from DE in AT, different ones apply there.

I do not understand the purpose of the stepping in a gable roof at all, for example, and here I also question whether you have understood or translated it correctly.

The idea is probably that setbacks are generally required, also with other roof shapes than the flat roof, but still in the manner of a staggered storey. For example, as "Tuscan style" that would also work.

In DE sind vollständig unterirdische Vollgeschosse irrelevant,

You omitted that the OP would like to expose the basement where it would be in the ground for an access driveway so that only the NW would have something like a ground-level house entrance – the rest would be the outer shell.

that the OP would like to clear the basement where it would be in the ground for an access road.

Worse: ramping up from the mountain-side street in a curve. Naively thought.

and above all to invest your money in something fixed with a clear conscience and not constantly just pay rent, which is a loss in the long run.

Hell no! That is really the only reason why you should not build.

You will never live as cheaply as in a self-built house again – the other reasons you gave have to be worth it to you. You only live once.

But please don’t think that you can expect less loss in the long term than when renting.

Especially not with the difficult plot of land and the necessary earthworks.

You have a logical error, you want to overcome the height difference from the street, which is then at least 2 m higher than the base level of your basement, within 3 m plus space in front of the garage with a 90° turn.

I had also posted a floor plan example with enough space on one level, which would, for example, also need to be clarified whether a hillside basement and 1 floor is possible.

Why do you actually need such a huge office for family use?

It doesn’t necessarily have to be within 3 m, we have enough space on the property, so if necessary we can make a longer but flatter driveway. Yesterday we dealt with the variant of a garage next door. Let’s see if I get around to tinkering with it today, then of course it would only be with a partial basement.

1 floor + hillside basement would of course be allowed, it can definitely be lower, but my husband has concerns that if everyone around us builds 2 floors plus hillside basement, we will be the “lowest” and the others will take away our southern sunlight. For me, I could imagine a hillside basement partly as living room/dining/kitchen.

At the moment, our current “office,” i.e., the second room, is the focal point of our home life. We both like to play PC games, my hobby is also digital drawing/design or watching DVDs on the PC. That’s why we wanted it to be relatively large since we spend the majority of our leisure/hobby time in it. Also, a large basement because my husband passionately tinkers with his 3 motorcycles/mopeds :) In case of illness/old age, an additional room on the ground floor (without stairs) is certainly also convenient to simply place a bed later. We actually don’t want it to be under 15 sqm.

It doesn't necessarily have to be within 3m, we have enough space on the property, so if necessary, a longer but flatter driveway can be made. Yesterday we looked into the option of a garage next door. Let's see if I get around to tinkering with it today, it would of course only have a partial basement.

A partial basement makes little sense on a slope, and I would always want to access a basement garage from the valley side. A comfortable ramp has a vehicle length flat at the top, the same in front of the gate at the bottom, and only 6° (= 10%) slope in between – up to here we have 30 m total length for a 2 m height difference – and it's straight. Just to access the garage from the uphill side, that would be too much for me. At 5 m width, that would also be 150 sqm of floor space.