Is it a parapet wall rising above the roof line? If so this would seem to be a common failure in this type of construction, only guessing but it could be that the wall upstand gets weather from both sides and therefore weathers more quickly. It should be a fairly straight forward job rebuilding the wall but only to the roof line and fitting a capping over the brick and roof edge.
Asbestos is relatively safe if untouched it is disturbing it that is the real danger and removing it is a specialised job.
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