Thanks for answer Karl Ottenstein!
I have solved your posting and few modify
First you must place the object in plan.Then select the object and hit 'ctrl+Shift+O'(option+command+o=mac). This opens the object. A dialogue box will then open and you will see on the left the parameters tab is automatically opened. Now select "new" in the top tab. This creates a new parametric function at the bottom of the list. In this new function – under the Variable column put "F" and in the Name put "Finish Thickness".
Make sure the type is on “length” and add 13(0’-1/2”=US Dimension) into the Value (default value – I have set to 13mm Plasterboard or Drywall for my American friends!)