Some will use 6 x 6 post and others use three 2x6's with the center 2x6 shorter to set the truss into so it is cradled. The belief is that a 2x6 plank is treated all of the way through and a 6x6 can only be penetrated a small amount (when it is pressure treated)
Morton buildings uses the 2x6 laminated posts. The quality of 2x6 lumber is easier/better/more controlled, and the resulting posts are far less likely to warp and bow than 6x6 posts. Plus the ease of making a drop-in support at the top for the trusses.
Morton also uses the 2x6 method to produce a sectional post that starts as a short 8'ish stub post. Four ft in the ground, 4ft out, which makes them much easier to install square and plumb than than a 16 or 20ft post.
The resulting above ground 4' stub has the inner or outer 2x6 piece shorter, and then the needed lenghth of upper post is set into it and nailed together.
It doesn't sound quite right till you see it, but it works, and Morton offers a lifetime wind damage warranty on their buildings, as long as the doors are closed when the storm happens.
Not a commercial for Morton, just that they used to build the majority of the pole buildings in my Dad's area. They aren't the cheapest, but are very good quality when done.
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