There are many policy forms and programs for contractors many programs present an inexpensive policy for contractors. While it may seem attractive at first glance you should ask your agent/broker if they are presenting the program that best fits your needs in the event of an occurrence or claim.
General Contractors, Roofers, Concrete or any other contractor that performs structural changes whether it be new, remodel or repair, you should look to an Occurrence Form program with a 10 year reporting period. Many agents/brokers present programs that limit the reporting period of the policy, which can become a major issue as many claims manifest years after the policy was written.
Policies that limit the reporting periods would be termed as "Sunset Occurrence Form," "Claims Made Form" and "Manifestation Form." It's best to always ask you agent/broker about the reporting period and to have it in writing on the proposal.