The parameter is per instance and doesn’t necessarily need to be a Shared Parameter via the component, you can create as many Project Parameters as you like and fill them in via RiR. The shared parameters can be used in Tags is its main advantage.
be aware that once you specify a certain type of parameter, volume for example, it expects a certain type of input, in this case a double (floating point number)
edit:
here we are getting the actual volume of the brep in the family and setting it to the parameter
