Moisture / mold in the house - call an expert?

Is what can be seen in the pictures a cause for concern?

Take a small pointed/sharp screwdriver (flat blade, or an awl) and stab firmly into the wood at suspicious spots.

If it easily penetrates the wood (wood is soft), then it is diseased!

If not, simply spray the beams|slats lightly with fungicide (respiratory protection!).

That should be enough.

Individual roof tiles can always be replaced from time to time.

Short update from me:

The waterproofing of the house and the drainage need to be completely renewed. Since the mentioned contractor is a colleague of mine, I can have this done for a maximum of 10,000 euros.

Tomorrow there will be an appointment with a friendly electrician who will check the status of the electrical system, and in the evening a building surveyor will come who has to approve everything or not.

Discussions with the bank were also successful.

If nothing surprising comes up tomorrow that ruins the plan, we will soon finally be homeowners.

Good luck!

The stains on the wood just look like typical old damage. As long as it is dry now, everything is fine - my amateurish opinion ;).