Maja

Sounds to me like you have a really sound basic building, but one which needs ongoing care and attention to keep it livable by our modern standards.

The roof.

It will work while you keep the terracotta tiles in their correct position.  However, if they move, it will leak.  If this is an ongoing problem, then I think you need to plan for some major works on the roof.  I think these would probably involve carefully lifting the terracotta units from sections of the roof (starting from the top and working down to the eaves).  Then lay a flexible membrane material over the timber.  Something like the Sika acrylic sheeting, with glue spots to hold it into position on the timber lining.  Once that is in position, then replace the terracotta units.  If you have broken terracotta units, you will need to find some replacements.  Maybe you could recover some matching replacements from other buildings where the roof has fallen in, or where somebody else wants to put a modern roof on.

However, others might disagree with my suggestions, so wait and see what else pops up.

As for the walls - sounds like you don't need to do too much.  If they are 1.5m thick, then probably not too bad.  Are the pieces of stone squared, or are they random sizes?  Are the joints between the stones filled with mortar or are they open?

What are the windows and doors like?

Cheers

david west