Floor plan design for a single-family house with a conversion option to a multi-generational house

No, but professionals who have studied construction planning for several years.

Why do I plan myself?

Putting rooms together does not necessarily mean "planning". Of course, it’s fun to be involved and to contribute significantly, but that leaves more work than you would wish for, but this:

Architects are not magicians either

.... is then a statement that will very likely trip you up. Because they are not magicians, they are called architects; otherwise, they would be called magicians. With your statement, however, you imply that you can do it just as well yourself… it’s not rocket science after all. If a street sweeper said the same about you and your job, you would surely be annoyed; but with your job, it is different. You do not respond to users’ questions and you are also an architect. Then I would say: Go for it – you can do it! By the way: There are many, many users here who have received excellent help; what could be the reason why it hasn’t been the case for you so far? My tip to you: Back to square one and try again with something new and informative… unfortunately without drawing €4,000.- with it

Try to separate the 1st floor and then still reach all rooms while keeping the ground floor layout the same.

But that doesn’t work. It’s not the first time we’re trying to think our way into designs.

Stairs fit on top of each other.

No! The stairwell on the ground floor is larger than the 1st floor room allows. The shower would basically have to be removed.

however, my wife and I have experienced that as well and we want to continue that way.

That’s why you’re building instead of living in a multigenerational house ;)

Why am I planning myself? Because I want to, I have the aspiration to create my own home, and architects aren’t magicians either.

But it isn’t good*. Your aspiration might be there, but you won’t do it justice.

I couldn’t think of anything better -

... *Stairwell already mentioned. And even if the stairs would work, the WC would be left out. If the storage room on the ground floor is to be a cloakroom, it should be planned in the front part of the house. If the technical room is in the utility room, then you basically have the freezer room accessible in the nice living area – that’s called poor planning because it’s not ideal. Storage rooms are completely oversized. The same applies to the bedroom sizes: Child 2’s room could be halved with almost the same living comfort… fewer corners on the 1st floor would give a better sense of space. The 1st floor is too convoluted. It looks more like someone awkwardly tried to arrange the rooms sensibly there, but it didn’t succeed. Windows are partly too small to be recognized as living rooms (room on the ground floor bottom left) Access from the utility room/garden is too narrow. Furniture sizes do not match the door sizes. Window in the bedroom does not allow for an adequate wardrobe wall. I’ll leave out the second floor – the one planned window can’t be installed anyway.

With your statement, you imply that you can probably do that just as well......it's not rocket science.

You're reading too much into it. But enough about that. Summarized again: - The house is to be used as a single-family home for now - Children (at least one) should have the possibility to move in later - We want to live on the ground floor in old age - The first upper floor should then (perhaps in combination with the second upper floor) become a separate residential unit - Budget for the house €650,000 - Basement for workshop, technical room for outdoor pool, dog shower

650k what should be included in all that?

Budget for the house 650,000€

Then deduct about 20-25% from the volume!