Final answer:
When two walls make a projecting angle, their roofs intersect in an inclined line known as a valley. The valley is the internal angle on a roof where two sloping roof planes meet, allowing for water runoff.
Step-by-step explanation:
When two walls make a projecting angle and their roofs intersect, they create a line called a valley. This is not to be confused with a ridge, which is the peak or highest point where two upward sloping roof surfaces meet. A gable refers to the typically triangular portion of a wall between the edges of intersecting roof pitches. The term hip describes a roof where all sides slope downwards to the walls, with a gentle slope.
In architectural terms, a valley is the internal angle formed by the intersection of two sloping roof planes to provide water runoff. Therefore, in the context of the question, the correct architectural feature described is a valley.