Hi,
If you want to create object for your model outside the Revit Default Family then you have to use "Create in Place" option. Please follow the path:-
Structure > Component > Model in place > select the object category ( Structural Framing) > give a unique name of the beam > Create > Extrusion/Blend/Revolve/Sweep (as per your beam shape is required). After creating the beam give the material as per your requirement.
This is very handy process to create a family as per your requirement. Hope this process would be helpful for you.
Thanks & regards,
Subhradeep Sen
Kolkata
India