Slate rooves are attractive but they require regular maintenance to stay ahead of potential issues.  The unusually harsh winter and the fact that we skipped having any work done last year has left a fair bit of damage to be addressed.  Our regular slater quoted us a staggering figure based on replacing 50 tiles.  A thorough, close-up survey of the roof with my drone revealed a far smaller number of damaged tiles.  The pictures should prove a compelling resource when I discuss the job with our guy.