To create an external/skirting plinth. You can firstly change your plinth recess under This design > Room settings > Plinth Recess. We recommend setting this to -15mm, which will bring the plinth forward from the carcass instead of back.

You can then change the style of the plinth by heading to This design > Attachments > Plinth > Change > Select 'Decorative plinth'. This should give you the 'Skirting' plinth look. See below:

These steps will achieve the look below: