leader for Cobia

I am planning to toss some flies at Cobia (hopefully) tomorrow morning. I have never fly fished for such large fish…nor have I ever thrown such large, brushy flies as the whistler patterns that I have tied…

Can someone give my some help with leaders…Do I use a 20 - 25 lb leader and tie in a shock tippet…do I build a more substantial leader? If I build, what test and lengths should I use.

I will be using a 9 wt rod with an intermediate line.

Thanks