After you buy a home, you almost always discover a few things you wish you would have noticed before. But while awkwardly-placed outlets or a dripping faucet may be annoying, issues with the roof can be expensive, frustrating, and damaging. So, to avoid surprises, you want to look very closely at a home's roof before you agree to buy it. Here are some things to look for.

Examine the roof for sagging.

A missing shingle here and there may not be a huge issue since you can generally just replace the shingles as long as the rest of the roof is in good shape. But a roof that is sagging is a sign that you should run away -- quickly -- from the home for sale. Sagging indicates that the wood that underlays the roofing shingles is rotting and damaged. It's not unheard of for a sagging roof to collapse, and there is most certainly water damage in the attic by this point. You should be able to tell if a roof is sagging just by looking straight across it. Be sure to do this on each side of the home.

Look for moisture in the attic.

Just because there are no missing shingles does not mean there are not leaks. Flashing, the metal that surrounds chimneys and vent pipes, can peel away from the roof and lead to leaks. Shingles can also become lifted off the roof just slightly -- enough to let a tiny bit of water in. To fully assess for leaks, your best bet is to venture into the attic. If you notice any moisture, try to trace lines of water back to their source. Or, hire a roofer to come take a closer look at to tell you if the leak is easily fixed or not.

Beware of moss growth.

If there is moss growing on the roof, it's best to look elsewhere -- unless you don't mind replacing the roof as soon as you move in. Moss is not just unattractive. It also eats away at the roofing shingles -- quite rapidly -- and is bound to lead to leaks if unaddressed. If you really love a home with a mossy roof, you may want to see if the owner will agree to replace the roof before you buy it. Then, you'll also have to address the conditions that led to moss growth -- like shade cast from a nearby tree.

Don't let roofing damage come as a surprise. Inspect the roof before you buy a home -- always!