pergola span redwood

Hi Y'all! I'm new here ;-) We build fences but were approached by an extremely well-known, regional business to build them a huge pergola in their parking lot. It could catapult our biz 10-fold and I really don't want to pass it up. But...I have zero knowledge of building pergolas and they...

Hello All, Given the design of this pergola using double and blocked 2x8s running 18 feet for the middle runs and the two end runs being supported by 6x6, is there any issues with the span for the middle runs? Using rough Redwood. <see attached sketchup done with Google Sketchup> Thanks, Moe