I have been asking the Factory for a "Tilt Wall Tool" for years. Still no luck, even in Revit 2012.
The current choices are:
1. Create a Mass, then convert the sloped face to a wall.
2. Create a special Wall Family, either outside the project or model in-place.
Good luck!
( PS--Jeff H. if you are watching, see--it's not just me who needs this!!! )