Also, you'll want to use screws when you install that final panel. It's far more trouble to try to clamp that huge cab up properly and get brads into it.
Much easier to pre-drill the holes as the plans describe.
What I did was trace the lines and pre-drill all the interior panels. Used screws on one edge and clamps to get everything sqaure. Then I screwed all the interior panels, and worked my way out from the screwed edge with the finish nailer.
If you're using cheap roundover bits that you don't care much about, they'll cut through 16ga just fine. But Bill's suggestion on the 18ga is a better solution.
As far as the screws go, chances are, you won't even need to countersink them, as screws tend to sink into pine. The pre-drilling just helps you locate those interior panels.
While I agree with Phatty on most of his post, I'd say using Arauco internally and BB externally is a great solution that will get your costs down somewhat, but afford you all the benefits of BB.
I'm a cheapskate, so I'll try out the cheap solution first... and usually end up crying twice
