I've purchased some beautiful FRP (fiber reinforced polymer) 8' colums to build a very large pergola, but I'm undecided about the top. I don't want to use wood. I wanted iron but can't get anyone to tackle something so large. Then I saw one exactly like my idea, only done with aluminum girders for both the headers and the crosspieces; it looked surprisingly terrific. I will be planting vines over it. There are architectural aluminum companies that make aluminum in a variety of colors (like bronze) that would look great. Any thoughts?