Complex profiles are the solution to creating different shaped trims.
Use the beam tool with a profile assigned to create horizontal trims, or the column tool to create vertical trims.
Once you have placed the beam or column you can easily change between different profile without having to remodel anything - just give it a different complex profile.
See the help files for more details, and this article gives some tips too -
http://www.archicadwiki.com/Creative%20Uses%20of%20Complex%20Profiles?highlight=%28Category3dModeling%29
Hope that helps.