Great Article from Do It Yourself

A leaking roof is the last thing that you need especially on a rainy night. Fortunately, you can prevent leaky roofs by following these simple steps, all aimed at taking care of the situation beforehand.
1. Check out the Most Likely Roof Leak Spots
The most likely places where you will get a roof leak are the chimney, plumbing vent flashing, ice dams, skylights, wall step flashings, furnace shingles, fields of shingles and missing shingles. It may be difficult for you to identify the problematic area in the absence of rain or snow and therefore you may have to do the identification during wet weather.
Apart from these leak hot spots, your roof may leak because it simply because it is worn out and needs a complete overhaul.
Most leak spots are never directly above the location where the dripping occurs on the ceiling. For this reason, locating the exact spot may require you to start in the attic. Here, you can locate a spot that lets in the sun’s rays or alternatively you can have a partner water the roof so that you can identify where the dripping goes through. Following leak stains is another way to find leak spots. Leak stains will normally be observed around skylights, chimneys, and vents.
2. Emergency Roof-Leak Repair Measures
Sometimes it just happens that a leak emerges right in the middle of a shower. You can take care of this by using plastic sheeting to cover the leak area on the roof. This sheeting needs to be stapled onto two 2 by 4s that can then be nailed along the eaves, climbing over the roof ridge, and some feet below on the other side of the roof. This should adequately cover the entire leak area.
3. Temporary Repair for Roof Leaks
Once you have identified the leaking spot you may as well start implementing some temporary repair measures. Such measures may involve climbing to the roof armed with tools like a hammer and some nails, and materials like tar and flashing.
Fixing the leak spot in this manner may suffice for a wet night but more repair work needs to be done if the problem is to be completely solved.
4. Repairing Leaks in Shingle Roofing
One of the easiest leaky roof repair jobs that you can do is when the problem is identified as bent-back shingles. Here, the solution involves replacing the damaged shingles. Remove the layer of shingles above the damaged ones and then replace them with new ones.
5. Problems with Collars and Flashings
Pipes are also a major cause of leaking roofs and the troublesome spots will mostly involve the collars and flashings. These immediately call for new replacements. Pipe leaks may also require some extra work in terms of observing if the wood beneath the roof is soft from water damage. Such wood surfaces do rot with time and thus they become unreliable. The situation may require you to re-roof the house depending on the extent of the damage.