leaking window

Hi Looked through previous threads and seems could be a few reasons, but wanted some simply explained bespoke advice on this please Leak coming into top of window when rains heavy (see red circle picture of entry) 2 bed semi property, downstairs kitchen window Can see on pics, and not sure...

We have a newly (extensively) extended bungalow with dormer type windows upstairs. They are 3 yrs old and the entire roof was replaced. The windows are aluminium double glazing and we have water coming in and staining the ceiling of the room below. the walls are rendered and there is no...