Loading Rebar Shape Codes in Revit

You need to Autodesk subscripted member to install the extensions of the Revit via subscription portal

Once you have install the extension for Revit 

Under Extension menu, for Tools select Content Generator

This will generate families for reinforcing bars & open a window Content Generator

Change the region to load standards specific to your region, go to file & select Regional Settings

Below window will open

Select Region & hit Ok, this will load the data

Once loaded select Reinforcing bar to check the data base loaded, check all the shapes you need in file and hit OK

Now you can start modeling Rebar in 3D with proper bar shape loaded either manually or with extensions