For first time this year water marks have appeared on the wall of kitchen just above lintel over window (water marks are running down from top of ceiling above window) the external wall takes all the wind and rain. There appear to be drip holes about 24 inches above lintel which suggests a drip tray but builder cannot understand why drip holes are so high above lintel over window. Any help or suggestions appreciated guys.

If you have weep holes I will assume you have a brick wall. Are the holes near the roof level? My guess would be an voice dam that allowed water to drain through the holes possibly a roof leak. Where are you located?

I think ma0641 was talking about an ice dam. This was certainly a winter more than capable of producing those.