http://www.animatedknots.com/albright/
With the Albright knot the heavier of the 2 lines is doubled (white in this video) and the lighter of the 2 (blue in this video) is used for the wrap. So in your case the mono would be doubled and the braid used to make the wrap.
As far as a top shot line, I would use a high quality floro carbon line like Seagar since Tuna can be line shy at times. There's been times that we've had to downsize as low as 30 - 40 pound leader to get them to bite.
Interesting when we were fishing for Giants with Tuna.com, they are very particular about their leaders. They use a barrel to join the leader to the main line, a crimp on the hook and stretch the leader after crimping it to the hook. Anything that is shinny like the metal on the crimps get's hit with a black sharpie to reduce it's potential for glare. Each time the leader is brought up they wipe it down with a piece of cloth to get any slime off of it as well. If the leader is on the deck and gets stepped on by accident it gets changed. Sounds extreme but I guess when you do this or a living, every little detail can increase your odds of a hook up and landing.
