Revit StructureSketch tools are available for manual placement of a rebar shape within a valid host. Rebar sketches will map to an existing shape when they share the following attributes:
If the sketch does not match an existing shape, a new shape will be created in the Rebar Shape browser and Rebar Shape type drop-down in the Options Bar.
Place rebar with sketching tools
Reinforcement panel
Rebar.
Placement Orientation (or Placement Perspective) panel
Sketch Rebar. 
Sketching a rebar shape
Optional. Click Modify | Create Rebar Sketch tab
Reinforcement panel 
Multi-planar to create multiplanar rebar.

Adding rebar hooks to the sketched shape

Mode panel
Finish Edit Mode to accept the sketch and place the new shape. The new rebar shape adjusts its shape by snapping to the cover reference. Rebar shapes that are bent in two planes can be sketched within a valid host.