Will construction material prices increase? Customs madness?

I would be quite surprised if Germany were independent of world market prices and supply conditions.

Then just don't be surprised if the prices don't explode. You can then brag at the regulars' table that you had the information a long time ago.

The work on the infrastructure won't start that quickly either; the earliest it will begin is next year.

It is no secret that my Generation Y now has to finance and put right all that the Boomers and especially Gen X have let decay for decades.

How could it be otherwise than that you are once again on the right and innocent side, a perpetually disadvantaged beacon, suffering under the stupidity of other people. And then came Superman.
Here, as if on a whim, an entire generation or even two are once again being blamed; previously it was teachers, then civil servants, the Chinese and Americans, but always pathologically blanketly the Others, which of course immediately makes one consider oneself on the right side—what else?
Such undifferentiated and naive argumentation should no longer be necessary nowadays, since through educational opportunities even accessible to everyone, anyone could know that such categorizations by humans (Generation xy etc.) are completely off the mark in many ways.
As my former boss said many years ago (also from such a guilty generation): "If someone is a jerk, then he is a jerk, no matter where he comes from."
And to stay with this dull choice of words, I would like to say: "What you are reproachfully whining about today in a blanket way, the Boomer generation settled during the lunch break with a stale filter coffee and a Gauloises in hand." (The discerning reader may please understand the thought behind this.) It is hardly possible to discuss constructively with those who categorize and sort people into boxes.
As was recently read here, when it comes to inheritance, you do not complain so much with widely outstretched hands about this unbearably guilty generation; then there is rather some pushing and shoving—oh dear.

I do think that the fiscal package and ReArm Europe will have an impact on prices/inflation. But not singularly, rather embedded in a global development. Should the declining interest rates, in combination with a general economic recovery, meet the fiscal package, then prices will rise more significantly. Demographic development on top.

The development is unlikely to be very uniform. Cement and burnt materials have a very high energy share. And they mostly come from regional production and depend on local energy prices. So the peak of 2023 is not in sight for now. I currently don’t see any major increases here. In the timber market, international demand factors, a tighter supply of high-quality roundwood due to infestation and environmental influences on the "plantations," as well as political framework conditions such as the enforcement of the EU deforestation regulation, play a role. I expect a slightly rising trend there. I am not an expert – this comes from my own crystal ball in my own information bubble.

The "customs madness", unless it is revised or amended - who can predict the next tweet - will probably have limited direct impact. We import few building materials from the USA.

The price of wood has fallen significantly along with other raw materials, but only back to the 2024 level. And to my knowledge, there are exceptions here as well, since the USA does not want to harm its own interests.

The more direct (negative) impact was definitely caused by Friedrich Merz's 'whatever it takes'. Especially at the longer end, interest rates have risen significantly. Here, Trump's policies, which might push the global economy into recession, rather have the helpful side effect that rates have fallen somewhat again. Especially at the short end. In the longer term, the market still expects slightly higher inflation due to increased government spending in the EU.

However, given the current situation, I would not speculate on anything. Everything is possible at the moment, from recession to inflation to the expansion of geopolitical conflicts.