Help with legal questions about buying a house

Questioner

Good evening, A month ago I bought a house. It is a municipal monument from 1750 with an age clause applicable. There is an extension from the 80s. Of course I had a building inspection carried out in which the roof was issued as 'moderate' but no specific improvement points/cost item was given. Now it so happens that since yesterday's rain I have had a leak in the extension. The seller stated in the purchase contract that there was a leak in the extension during inspection where they replaced the lead fittings on the roof and cleaned the gutter. Now this is a leak that is not related to the lead or the gutter. I have now exchanged messages with the seller who indicates that he has often had problems with damp patches during heavy (driving) rain. This is not stated in the purchase contract. In the meantime I have had a roofer over who indicates that the repair will cost around 1500 euros because, among other things, the battens are rotten. In addition, there is plastic under the roof tiles, which can cause further rotting because it is not breathable. The entire roof must therefore be dug up to replace the plastic with breathable foil and to replace the battens/roof battens. My question is: should the building inspector have seen/investigated this? It is visible when looking under the roof tiles (from a staircase). If not, can the seller be held liable since he knew this but did not report it? I am not looking forward to long drawn-out matters, but it is a fairly expensive repair for a house that I just bought and a problem that did not arise in the past month. Hopefully someone here can answer my questions!

Lawyer

The building surveyor should have reported this, which indicates that the 'investigation' was not done properly, which means that if you had known this before the purchase, you could have confronted the seller with it.