In general, such questions are clarified before moving into a new home, but okay. First of all, you need to understand what exactly is the problem, is there holes in the roof? is it rotting? is it leaking? If you just do not like the appearance and you need to repaint it, you can do it yourself. If the issue is more serious, in this case, people turn to sootvetstvuyutsya services, from personal experience I can recommend https://www.crosbysroofinginstallers.com/, they are real experts, not once helped me out in similar issues, the most pleasant prices and high quality on a par with the efficiency of the work, very adviseable
