Is a Riester loan useful for my case?

If you’re willing to live with €10 laminate and €10 tiles, it can work. You can also get cheap hardware store doors for €200. But you shouldn’t expect much, and even then I’d say it’s going to be tight. How did you calculate the amount? Or is that a rough estimate?

That was roughly estimated. Of course, I still need to go into detail. I created an Excel sheet for this. For example, I calculate around €4,500 material costs for the flooring on the ground floor. Carpet upstairs with €2,400.

I only planned doors for the kitchen and bathrooms: about €1,500, totaling €8,400. The only thing I am not familiar with yet is the cost for walls. But I think I can make a good compromise there. Just like the bathroom: it doesn't all have to be Villeroy & Boch. The standard should be sufficient here. Unless someone can tell me that I absolutely have to buy Villeroy & Boch. If that can be reasonably argued, I am happy to consider it.

I also only budgeted about €10,000. Let's leave it at €15,000 in the end...

I put together a detailed Excel. There's already a lot of work in it. It's far from complete yet. But this mentioned sum is foreseeable.