Floors, Roofs, and Ceilings - Autodesk Revit Architecture 2015 Essentials - page 71

Figure 3.17 Roof sketch and slope properties
7. Finish the sketch, and look at the project in 3D.
Although the roof begins at Level 3 and has the proper slope, it's
immediately obvious that the walls don't extend up to the roof.
8. To resolve this condition select all the walls (using the Tab key to
select the entire chain), and set Top Constraint to Level 4 in the
Properties palette. The results resemble Figure 3.18.
Figure 3.18 Adjusting the wall height
The objective of the following exercise is to create an extruded roof and join it
to an existing roof.