In the CADclip below I demonstrate how to create the custom column family shown above using the column.rte template, one solid extrusion and one void extrusion.
The only part I did not get time to explain was the 'materials' aspect which I have covered in detail in many other CADclips. Youtube limits videos to 10 minutes and I just could not squezze it in.
To do so:
Create a new instance parameter named 'column material' and make it a 'parameter type > 'Material'. Then associate that parameter with the extruded column's material property. Then load it into a project and change the material as required in the project. Making it an 'instance' parameter allows you to change the material of each inserted column family. Otherwise you can make it a 'type' parameter for more global control.