In Revit 2013, you can’t tag the slope of ramps in Plan views using the Spot Slope tool.  There are workarounds out there already, but here is an easy one:

  1. Make a new Generic Model Adaptive family with 2 Placement Points
  2. Make a spline between these two points (select them and then hit the spline by points button).  Set its category to Invisible
  3. Load this Family into a Project, and using a 3D view, place it at the centre line of a ramp (the two points should snap to the correct location in 3D)
  4. In a Plan view, use the standard Spot Slope tool in Revit – just pick the adaptive component “line” that you just placed.

EDIT 
As I mentioned above, there are other workarounds for this. One is to put a slope arrow on an adjacent Floor, then copy it on top of a Ramp. It works!

Check out comments and video link below…

Link:
http://www.youtube.com/watch?feature=player_detailpage&v=IJD14dDUKbU#t=71s

I actually found this did not work too well in Revit 2013 (no problem in 2012).  However, after a bit of fiddling, I have created 3 files (one for Revit 2012, 2013 and 2014) – all of which have spot slopes on Ramps that can be copied around.  Here is the link:
View / download