It can be very difficult for you to know for sure if your roof is damaged in any way. Perhaps you have a leak and even then it could just be leaking into your roof space, how are you to really know? Unfortunately, it is a problem for a lot of houses and they are taking on water damage and other problems without them ever knowing. The best way you can know is to actually get up on your roof and check it out yourself, and this can be daunting. If you own a ladder you should get up and have a walk around, obviously be very careful or get someone who would be confident up on the roof to go up for you. While you are up there, there are a bunch of things you should be looking out for.
What to look for
On a tiled roof make sure you are only stepping on the bottom of each tile as you walk around. You will be looking for any cracks in your tiles or maybe even a whole sections of tile that are broken. If you take your time looking as you walk around the roof and find out just how many of your roof tiles are broken. For a shingled roof keep an eye out for shingles that are curled or buckling, also check to see if any shingles are losing granules which may mean the shingles are nearing the end of their life.
Have a good look around the valleys on your roof (the area that lets the water run down the corners of the roof) look around them for any damage or debris, you also want to check down the sides of the valleys and make sure there is no way water can get through. The valleys are one of the most important areas of your roof, snow and rain flow through them so you definitely do not want them to be compromised in any way.
The chimney on your roof (if you have one) can be another problem area, that and any surface next to a wall. Make sure you have a good look around these areas, any flashing around the roof needs to be undamaged and secure. Make sure it is all looking ok. If you have access to your roof space that can be a good way of looking for any light that is showing through. One other thing that you can do while walking around your roof is just to make sure it all feels secure, any spongy feeling underfoot may indicate damage to the battens in your roof.
Overall I would not be worrying about your roof on a newer house, but most houses people are living in are at least 10 years old. Any house that is starting to get 10 years old or older will probably start to have problems with their roof. If your roof is at this stage it can definitely be a good idea to hire a professional to come in and have a look around.