There are a lot of factors in knowing if you need a new Roof, some might think u need a new roof but maybe you can save a little money and just repair it? If the shingles that are on your house right now have a loss of color and or granules from what they used to look like, you will most likely need a new roof, the granules that are on the shingles are there for a reason so if gone there will be problems. Also if the edges of the shingles are peeling up and even cracked on the edge then that means that either the shingles are very old and leaks will start happening very soon. Most old shingles were made for a 15-20 years lifetime, so around that time, u might need to be thinking about getting a new roof installed onto your home. If your house had recently gotten a roof replacement most all the new shingle companies offer a way more durable shingle that will last a lifetime.