A very common spot for your roof to leak is at the chimney. a damaged chimney crown can allow moisture to penetrate the brick itself and work through the masonry. Water can get thru shingles around flashing or can be leaking through the flashing itself.
The first step in correcting a leaking chimney is to identify where the leak is coming from. There is nothing worse than paying a roofer to fix your flashing only to find out that the moisture was penetrating through the brick work itself and not the roof. There are a variety of ways to fix a leaking chimney. Sometimes all that is necessary is caulking in the flushing, sometimes just attaching the chimney crown. what's a burka become overly saturated and are allowing moisture to flow through them, more drastic steps may be necessary.
are you even seen it after a chimney has been rebuilt where it still leaks because the brick used allowed moisture to penetrate them. The brick were not properly rated to resist, moisture or shifting freeze and thaw cycles. A great solution to this is to install a rubber membrane or through wall flashing through the masonry itself, addition to this forming and pouring a chimney crown with a through all the flashing or rubber barrier above the masonry also will ensure your chimney never leaks again. well these last two measures are much more drastic and more involved, they have been proven time and time again to provide a leak free chimney.