Earlier one of tiles on our external vertical tile hung wall, which covers first floor to roof level, fell down and broke, although we can only find part of it so assume the part with fixings is still there. On inspection it looks as if there are also two others missing on different walls, at least one of which has part of the tile still in situ. Googling suggests that the tiles above need to be removed in order to replace the broken one (irritating two are relatively low down). Can anyone please advise how big a job this is likely to be and what type of trade would do the repair - a roofer perhaps? We have some spare tiles but just not sure how to proceed.