How much more does one pay for "fixed price"?

I don’t know if this helps you as a reference point, and it really *depends* heavily on your demands and wishes.
Back then, we approached building the house mentally and said, "we just want a home, what’s in the construction specifications is actually enough for us."
Over the months of preparation and planning, "that’s actually enough" quickly turns into "you only build once!"
You always have to keep the total price in mind and shouldn’t get too carried away by the nice-to-haves.

I asked a friend who had built a house back then, and he said, "Add another 30% on top of the final price, then you’ll be about right." I thought, "no way!" But in the end, that was pretty accurate. There’s no point in sugar-coating the numbers.

We were at (all approximate figures):
Land price: 78,000
Catalog price house (solid construction specification): 228,000

Final rough cost planning (rough cost breakdown): 432,000
My Excel sheet (as of today) where we will actually end up: 445,000 - 450,000
(including everything known so far, kitchen, moving costs, necessary furnishings, paving)
We neglected the garden (often forgotten, by us too), and if there would be 10,000€ left at the end, we would definitely spend that on painting work.

So, for us, another 45% came on top of the "land price and catalog price."
You can certainly manage with 30%, but I would definitely calculate that for additional costs, etc. It always depends on the circumstances, the condition of the land, the construction specifications, what you want, how handy you are - basically, you have to calculate it yourself, every building project is individual, our numbers should serve only as a reference point.

Be assured, no housing provider ties up capital to buy you out of a plot.

Although it's been a week, you can change the "no" to a "hardly," unfortunately, it plays out exactly like this in the town here, that plots are bought up in stock by one and the same company, even on a whim, as long as they "have" it...