Drawing FBDs for Ramps
Choose the object of interest and draw it as a dot or box
Draw and label all the external forces acting on the object
Sketch a coordinate system, choosing the direction of the object's motion as one of the positive axes
Pseudo-FBDs
When forces don't line up with axes, you can draw a pseudo-FBD
Break forces that don't line up with axes into components that do
Redraw your diagram with all forces parallel to axes