Customising Beam Elements as Double layered Timber Gridshell

Hi All, 

I am working on optimising a timber gridshell with supports on 3 sides in a predefined surface.

I wanted to know how to customise the cross-sections such that I can get a double layered Grid Shell of 60x60mm th wood battens.

I currently have a grid composed of individual lines but if i will be needing a lath member of say 6m length. How can i feed in this information to karamba?