Hi I recently brought a house it has a side extension garage which has a felt flat roof which is leaking, the flat roof is poorly done but the house has a side window which is large and preventing getting a good seal Between the roof and the house. Also underneath the window is a dead space no bricks? Any advice would be great I’m planning on getting tradesmen to help removing the old window placing new bricks and plaster and render and then a new smaller window, then new roof adjust the fall so that there is no pooling and getting a better seal between the roof and house any help or advice would be much appreciated,