Professional roofers tend to be called out when there are problems such as a leaky roof, a fallen tree limb, or some other sort of damage. This is not the only time that you should call someone out, however. The best roofing companies will give you free inspections and you should take the opportunity to have them inspect your home about once a year to make sure that there is nothing potentially developing.
Roofers can perform a thorough inspection of the roof and attic to ensure that there are no issues and that there is proper ventilation for the roof. Not only should a roofing company provide free inspections, but you should not feel obligated to purchase anything. This means that the really professional roofing contractors out there will not hassle you into buying a service and will simply tell you if nothing is wrong with your roof. They will earn your trust and then you will call the roofers when you actually have a problem.