A look at how the combination roof offers you two roofs for the price of one
A Combination Roof, as seen on a branch of Pizza Hut. Image by George Sheldon (via Shutterstock).
Strictly speaking, it is possible to claim that any structure with more than one roofing type has a combination roof. A hip and valley could be seen as one; a gable and shed roof, likewise; a lean-to and skillion roof, even more so.
The above are correct, but the most common perception of a combination roof is a gable roof with a hipped roof at the bottom. If you go to a drive-thru McDonalds or Pizza Hut, the gable roof and hipped roof combination is ubiquitous.