One to two times a year, you have to go up to check if the drainage is still clear. If there are many deciduous trees next to the house, the effort increases. Without trees, it decreases.
In my opinion, you can also do this yourself. Provided you are not afraid of heights and have a good ladder that can be safely set up. Depending on the height and other conditions...
You could non-bindingly ask a roofer what an annual inspection would cost you.