How do I finance and build correctly? Solid house or prefabricated house?

No, not for me. A gable roof can be constructed as either a rafter or purlin roof. Both have advantages and disadvantages. Sometimes one is cheaper, sometimes the other. For example, if you build a knee wall, a rafter roof is not possible. If you want to cover a long room without supports, a rafter roof is more suitable.

That's not true, I have a rafter roof with a knee wall of 1.5 m!
It's only the ring beam that matters!

Short question, or rather my suggestion for the OP. Shall we provide the financing assistance here

[Baufinanzierung Forum - Allgemeine Fragen]

and conduct the construction discussion in one - possibly someone can make a suggestion regarding the thread - a dedicated thread for that?

It was not about financing, only about possibilities.

Then you don't have a rafter roof, there are also other types of construction that are uninteresting for today's [EFHs].

Then define it and justify it!