Rain Leak Source Diagnosis

My residential home has a pitched roof and, whenever we get heavy rain, water finds its way in right around the window frames. I need a specialist who can spend time on-site, trace the exact entry path, and tell me plainly whether the roof, its flashing, or the windows themselves are to blame... (Budget: £250 - £750 GBP, Jobs: Construction Management, Photography, Report Writing, Roofing)