I had recently my loft converted and same time had roof felted and re-slated.I had three sky lights fitted.While builders were still working ,past few weeks heavy rains one of the sky lights started leaking.Water seems to appear right at the bottom of it on right side corner.Builder has been on roof few times ,says can not see any thing wrong.Water leaked at least 3 times previously.Last time he has been on roof with silicone.He said there was a hole in slate and it is fixed.We had heavy rain today and it started leaking same spot again.I believe water is escaping from around or above the sky light,running down the the felt and finding a hole in felt to escape.I have told him no more silicone.I want window to be stripped down to have a look what,s wrong.What could be likely cause.