Felt Roofing and Slipped Slates

A property I am in interested in buying has felt roofing on the kitchen extension. The rest of the property is slate roofing and a few due to the high winds have slipped (the slates look pretty old too). As I cant even be described as a novice in this area I would be greatful on any information on these issues as well as rough estimate on costings before I proceed to buy this property and find I have a £10,000 or so repair job on my hands!!

Any help on this matter would be very much appreciated.

Slates looking old does not mean they are knackered.. However slipping slates indicates the nail securing them are corroding.. no easy fix for this. Any chance of a PIC?

I feel like I have discriminated the old slates! Nothing else is wrong with the roof apart from one or two slipped slates. After finding more information on this I think we can fix this without too many problems.

Many thanks for your comment and tip on the slates.