Working on your roof will likely be a difficult job if you are afraid of heights or if you aren't sure of how to place shingles or repairs needed to stop a leak. This is when you can call a roofing contractor to get the work done for you so that it's done right. Aside from a leak, there are a few other reasons to contact a contractor.
If there a small black particles when you clean your gutters, you should probably consider calling a contractor. There particles could be a sign that the shingles are falling and losing pieces that will hold them in a place. Some shingles might blow away after a storm, or there could be damage from hail. Missing shingles could be easy to replace, but there might be damage underneath the shingles that you don't see. The contractor can examine the roof to see if there is anything underlying damage before replacing the shingles.
Pay attention to the decks or carport outside. Some water leaking from the roof is common, but if you continue to see water dripping from the roof, then this is likely a sign that there is a leakage allowing water to reach the lower levels of the roof. This can lead to a hole being created if excessive water comes through. Some shingles might look like they are popping off of the roof. This can allow wind to get underneath the shingles, causing them to blow away. It could also mean rain gets underneath the shingles. Another reason to contact a contractor would be if you want a different style of roof, such as metal, or if you are modelling a home and need to add a new roof because the current one isn't in good condition for the home.