All flat roofs are a pain, you need to make sure the roof is clean & a layer of mineral felt applied with a coat of one of the marley products designed to be used cold, the roof is painted just enough for each strip of new felt to be applied pointing towards the lowest edge usually the gutter The next strip is then applied with a 3inch overlap laid again towards the lowest point ,if the fault is next to the wall a strip of flash band or similer flashing tape is laid half on the wall & half on the new felt in a L shape, make sure you are safe working at hights before attempting this & dont scimp on safety.small patches will not be succesful because the sun will bake the bituminous compounds & crack it. hope this helps Terry
Terry Howell, January 2010