SURFACE PATTERNS FOR RAMPS IN REVIT

No you're not doing anything wrong. Revit won´t display ramp surface patterns in plan views. It will however in 3d views. So how do we overcome this bad joke?
In your plan view, right click on the ramp and select "Override graphics in view". Under "Surface Pattern" choose the one you need. NOTE: it will only let you choose DRAFTING patterns, but that's much better than other less convenient turnarounds.

OVERRIDE GRAPHICS IN VIEW

RAMP WITH DRAFTING PATTERN APPLIED

Here´s a link for more tips and solved mysteries about ramps::

SLOPE AND OTHER PROPERTIES IN REVIT RAMPS