I have 2x6x16 rafters hooked in to the side of my house. There will be approx. 12 of these. I have three 6x6x8 post that will be cemented in the ground. As of right now I have a 4x6x20 going across the three post to hold 2x6x16's plus roofing. Will this 4x6x20 hold the weight?