Do you just look through the different specs and find a card that you click with and look for other cards that have synergy with it? Or perhaps, you like the artwork on specs that you have chosen. Maybe you got victimized by a particular spec and now want to try it out? Perhaps you want to build a codex around a particular keyword.
At this point, I’m not convinced there is a right way to construct a viable codex or for that matter that not all codices are viable. I haven’t played enough where I can form an informed opinion.
I like the idea of playing random specs and having to adapt on the fly, but at the same time like to think about some of the nasty spec combinations that exist.
So what system do you use? As for me, I try to use a different system each time I go about selecting which specs I want to you.