Hi Laura,
Not being able to see the actual problem it's hard to say if this is a good quote or not but based upon experience of having a simular problem and paying €400 to get it fixed I would say this is a good quote. I also had some slates come loose and a slate that was totally blown off my roof last week and I was charged €250 to fix the problem so I would say this quote is OK. As always it does help to shop around.
Regards,
Dinging.