The structure of a roof can vary depending on the design of the building and the materials used, but most roofs have a similar basic structure consisting of the following components:

1. Rafter: One of the sloping beams that supports a pitched roof. 

2. Purlin: A horizontal beam that provides support for the rafters of a roof. 

3. Underlayment: The underlayment is a layer of material that is applied to the roof decking before the roof covering is installed. It helps to protect the decking from moisture and provides an extra layer of insulation.

5. Flashing: Flashing is a thin strip of metal or other material that is used to seal and protect the joints and edges of the roof from water infiltration. It is typically installed around chimneys, vents, skylights, and other openings in the roof.

6. Ridge Vent: A ridge vent is a type of vent that is installed along the peak of the roof. It allows warm air to escape from the attic or roof space, helping to regulate the temperature and prevent moisture buildup.

7. Roof Trusses: Roof trusses are pre-fabricated triangular frames that provide support for the roof decking and the roof covering. They are typically made from wood or metal and are designed to distribute the weight of the roof evenly across the structure of the building.