How to create Parallel beam family

[wfrst2008]

Hi all,
I want to create a double beam family, it seems to me that
it should be quite straight.
It is basically successful, please see the attached RFA file.

However Revit does not allow me to :
1. revise the beam gap parameter
2. change type of beam.

What I have done wrong in this family ?

rgds
Fung

[wfrst2008]

just viewed this web page by chance,
seems my query has no solution yet.

http://revitoped.blogspot.com/2011/0...y-puzzler.html