A roof can suffer from various types of issues. Moss is one issue that plagues some roof shingles. If your roof looks worn out or bad because there is moss growing on your roof and roof shingles, don’t jump to conclusions about needing a replacement roof. In many cases you can actually clean the moss from the roof and the roofing material will end up looking much better.
Sometimes moss grows back, so it may be an ongoing effort, but it is definitely worth looking into this, because it is much more affordable than getting a new roof installed by a roofing contractor.
Here is a link to an article on the getting moss off of a roof.