By Dennis Collin
When dimensioning along or across wall elements that are not parallel or perpendicular, use the TAB key to pick a wall intersection point. Look for a tooltip on the status bar that describes two intersecting walls, before clicking the first-dimension reference point. The dimension object will then follow the desired direction.
The status bar located at the bottom left hand corner of the screen is often forgotten by many Revit users, but the bar is very useful in this case to get dimensions to measure lengths correctly.