I'm building a sun cover for my open air atrium. Dimension is 8x8 ft. I'm building with clear cedar(ver expensive). In one direction, I'm placing 19 8ft 2x4 cedar boards tilted vertical and spaced 5 inches apart. Knowing the boards spanning 8 ft, anchored at both ends to the square frame, will sag as moisture penetrates during the winter. Question. I want to place on top of the 19 boards a stainless tubular beam! At the mid point and perpendicular to the 19 boards. The beam will attach via screws every 6 inches. The weight dry for each cedar board is 6.5 pounds. What should be the dimensions and thickness of the stainless (or other metal) to ensure support of these 19 boards? How do I factor holes drilled and water weight of boards? Any takers on this? Thank you!