One of the most common problems in a flat roof is that there are low spots. Much of this has to do with the fact that there is very little drainage. The water from rain starts to pond onto the various areas of the roof. Over time, the weight of the ponds starts to create low spots. This can cause leaks and various other problems. The only way to overcome the low spots is to fill them in. This will help to keep the roof flat, without any holes to cause ponding and pooling.