Single-family house with flat roof from 1968 / renovated in 2013

Unfortunately, it doesn't make any sense to tell you something that doesn't hold water. If someone now says, yes, you can remove the mold for €30,000 and the roof costs that much again... what does that bring you? Nothing. Because that would be a wild guess. Plans for the house are available at the building authority or not at all. For ours, there were no plans left, only one drawn by the previous owner. Wiring plans are mostly only for newer houses.

Well, it would at least be an estimate of what a renovation of the flat roof and possibly house insulation roughly costs, or a moldy basement room to renovate, or to sand wooden floorboards... In countless other threads, there are also estimates.

With old buildings, you only really know what you have once you have bought and damaged it. Then more things come to light. More unforeseen problems. Perhaps pollutants. Woodworm, dry rot. Different structures/materials than previously assumed. Suddenly you can't remove this or that wall after all, or there are pipes inside. Quotes differ massively from estimates. I can tell you from experience that with an expert you get the best preliminary assessment and have to accept all further surprises. Plan a generous buffer for this.

And in your case we have no floor plan, no pictures, nothing at all. What is there to estimate? Flat roof according to Google around €30,000 give or take. Maybe you still can't find a roofer for under €40,000 or you find one for €20,000. What external insulation costs Google can tell you roughly as well as anyone here. Approximately €200/m2 according to Aunt Google. But then there’s the exterior plaster and all kinds of extras. That all adds up to high five-figure amounts.

And if the seller is being overwhelmed like that, then you don't have time to wait another week for statements in a forum. Back then, we had the expert (my uncle^^) on site within 2 days and confirmed immediately after the appointment, verbally on site and then by email 5 minutes later. Then another 2 days or so for the bank's approval and then we got the contract. Due to sympathy and speed.