Roofing work is generally not a DIY project. Professional roofing contractors are trained and benefit from years of experience to safely & effectively repair or replace your roof. An untrained homeowner can actually harm a roof with improper roofing techniques and could even harm themselves if the right tools & safety equipment are not used.
Simple maintenance tasks like inspecting a roof during the spring to look for broken or crack shingles & cleaning out gutters filled with debris are suitable for most homeowners but should still be done with care. Most DIY roofing projects end in additional costs & headaches for the homeowner, so they are best left to trained & experienced professionals.