Water damage bathroom attic / roof and house purchase

Hello everyone,

we viewed an RHM (built 2004/5, solid construction) in the Rhein-Main area. The house has water damage, it was dripping in places, which could be clearly seen on the facade - see picture. In the bathroom in the attic, there were even mold spots on the ceiling (unfortunately I did not photograph them). So it comes from the roof. Unfortunately, the real estate agent gave very little information about it; he estimated the repair costs at 15 to 20k€. The owner naturally wants to sell the house as quickly as possible and would be willing to negotiate on the purchase price...

Since we really like the location, we are considering whether it might still be worth being "bold" here. Obviously, it would make sense to bring in an expert, but first I would like to ask for an assessment of the damage here. Maybe it’s not even worth hiring an expert (meaning: just forget the offer)...

I look forward to suggestions/comments, many thanks in advance!

Flat roof with an internal gutter? only the connection to the gutter is defective? painting the facade alone already costs 15-20k€. If the entire roof is leaking broadly or water is behind the [Vollwärmeschutz] or the ceiling (material?) needs to be renovated, a few more € will be added.