Not sure what trade category to choose for the below

Our property is a 52-year-old, mid-terraced, flat-roofed house with cavity wall insulation. We have a leaking bay window ceiling which is damaged to the point where it needs to be replaced rather than repaired. The leaking seems to occur during wind-driven rainy weather, or prolonged showery weather with relatively no wind. The bay window is fitted with blinds, and water leaks through holes in the ceiling where the blinds are attached. The bay window is of uPVC construction. The source of the leakage is not obvious to me, so I am looking to select the right tradespeople to investigate and solve this problem before having them replace the ceiling. My suspicions are ingress through: the window sills above the bay window; the lead flashing; porous brickwork above the bay window. Cavity insulation was pumped into the walls about 25 years ago.