This is a difficult question to answer, as it largely depends on the amount of leaking, how long it has been leaking and what materials your roof is made from. If it is a new leak, it may be able to be “patched” in some way, without worry to the damage underneath. If the leak has been occurring for some time, there may be damage to the crawlspace or attic of your home, which may mean that section of the roof must be removed so that the area underneath it can also be repaired.
This is another one of the main reasons why it is essential to have your roof inspected routinely and then to fix problems quickly once they are noticed instead of waiting. Water damage in the home can harm more than just your roof, it can cause a mold infestation and damage the actual foundation of your home, leaving you with much higher and avoidable home repair bills.