You must not have used a very good roofer if they replaced everything and it still leaks?
A competent roofer or good general contractor should be able to figure it out for you relatively easily. Now, they might need to try 2-3 different things before they get it solved, but a competent individual should be able to handle it. Hard telling what it is without seeing things first hand, but it could be the roof, the wall, windows, flashing, penetrations, etc.