I am going to build a free standing roof over my deck. The measurements are 12'x21'. Should I use 4x6 posts anchored in cement? Or 4x4's? The deck is above the ground 32 inches.

Can you tell us where you live. We'd need to try to access the building codes for your town to give an accurate answer. Are you thinking of anchoring the new posts to the deck or will they be outside the deck foot print and go all the way to the ground? How many posts alomng the 12' edge and also along the 20' edge?

I live in Louisville,Ky. I was going to put 3 across the 20' side and 2 across the 12' side . I was going to put them in concrete in the ground. I was going to use a metal roof which is pretty light. And I'm going to use 2x6 rafters. On top of the rafters would be 2x4's every 3 ft. spanning the 20 ft length to attach the metal. I also didn't know whether to use 4x4 as beams resting on top of the poles, or 2x6 or 2x8 as beams.

I live in Louisville,Ky. I was going to put 3 across the 20' side and 2 across the 12' side . I was going to put them in concrete in the ground. I was going to use a metal roof which is pretty light. And I'm going to use 2x6 rafters. On top of the rafters would be 2x4's every 3 ft. spanning the 20 ft length to attach the metal. I also didn't know whether to use 4x4 as beams mounted on top of the poles, or 2x6 or 2x8 as beams.

Came across this and thought it may come in handy for your job. Span Calculator (http://www.cwc.ca/cwc/Template/SpanCalc.aspx?NRMODE=Published&NRORIGINALURL=%2fResources%2fE-Tools%2fSpanCalc%2ehtm&NRNODEGUID=%7b41B9325F-527F-42E7-9D91-3BCD0359AA93%7d&NRCACHEHINT=Guest) Do you ever get snow in Louisville, makes a diffference in these calcs