Two story front porch/deck question

Hi, I was wondering if anyone could tell me if you should put decking down first and the the columns on top of the decking?

I have a 2 story front porch and I replaced the lower 4x4's with round columns. I am now going to replace the upper decking and the 4x4 posts holding the roof up. My question is, should I put the new decking down first and then put the new posts in on top of the decking. The old way was the 4x4's were put up then the decking was cut to fit around the posts.

I see some pics of houses with front porches that hve the posts both ways.

Thanks in advance!

Tom

p.s. The lower porch was replaced with concrete. ( not that that even matters)