A Virtual House - Google SketchUp Workshop: Modeling, Visualizing, and Illustrating - page 177

FiG 10.6 Cutting the walls using the roof pitches.
Tip
Choosing the Intersect with Selection option instead of the straight
Intersect option places less stress on the processor and produces a
quicker result.
To produce the roof thickness, the Push-Pull tool was used on each of the
pitches. Guidelines were used to locate the precise intersection of the ridge
line. The upper edge of a single pitch was selected, then, using the Move tool,
the end point of the edge (look for the green Endpoint snap dot) was moved
until it snapped to the intersection of the guidelines.
FiG 10.7 Push-pulling the roof pitches directly in the Z axis.