Is basic damage insurance a must?

Ok... those who can read have an advantage. You are right.

I now have an offer that reads well except for the residential building insurance new building discount [Neubaunachlass]. Graduated scale: 1- years 40% 15 - years 0% Is such a discount scale usual and does the insurance generally become more expensive over the years?

What do you care about percentages? What matters is what is at the bottom line.

I now have an offer that reads well except for the residential building insurance new construction discount
Scale:
1- years 40%
15 - years 0%
Is such a discount scale common and does insurance generally become more expensive over the years?

It is common.
This concerns the age of the building.