Construction costs are currently skyrocketing

Just draw it out when you have trouble imagining it in your head and then see which lengths you need to lay and, above all, which direction. Sure, there will be a board "cut wrong" sometimes, but everyone goes through that.

During my apprenticeship, tons of cables, metal pieces, etc. were thrown in the bin because you have to practice before you can do it. I still can't weld...

I think you’re also making the mistake of believing that craftsmen always do professional and above all perfect work.

No, but I’m not so arrogant as to believe I can do everything at least as well as someone who has learned it and does it every day. If the craftsman makes mistakes, he fixes them. If I mess something up, I pay twice – in material and time. In our old house, I plastered a wall with a concrete look myself because I occasionally like to do things myself and because the 2,500€ the master painter wanted for it was too much for me. He would have certainly needed half the time and done it more perfectly than I did, but I didn’t care about that. For other things, I do care and then I let the craftsman do it and have it corrected if necessary. But aside from skills and willingness, you also have to consider when it’s worth it and when not. But everyone as they want and can!

Yep. But that is exactly the reason why many can no longer build or ultimately run out of money. Because everything has to be done by the craftsman. Then please don’t complain.

Oh, I see. And it doesn't always have to be 100%... the beautiful white wall will already have stains after a few weeks with children...

And craftsmen who do repairs? Do those still exist?

Guys, I envy you... especially those who do a lot themselves... you can watch stuff on YouTube and still end up standing there like, "how do you start now" or something like that. If you have someone who helps out, it’s a different story. Unfortunately, I just lack a certain mindset when it comes to craftsmanship. :( I have tongue and groove boards on the attic floor... they really should be properly installed... I’d like to do it... but I don’t really have a clue how to start... that bothers me... Better to postpone it than start wrong or something...

With a bit of information, you really can’t do much wrong. And if you do, you can always correct it. This is the best place to practice.
Do you want to cover the whole floor? What kind of subfloor do you have?
On an attic floor, probably the roof trusses or rafters? You can screw directly onto those. Buy floorboard screws, screw into the tongue. Start on one side, screw the board in, then the next one, screw it in again. Leave a 1 cm gap wherever it borders other components. Lay it staggered like laminate.

The beams running from eaves side to eaves side, approximately 90cm apart. Between them, the insulation. This raises the question, for example, whether to screw or nail directly onto it. Then I already heard from neighbors about putting another battens on the beams to get it a bit higher, I think because of the distance to the insulation. Another says directly on, no raising… well, how is it done correctly… yes, the whole floor, up to almost the sloping beam (ridge - eaves). The tongue and groove boards are almost the right length. I think the longest were 5m, so an offset is hardly possible.