Depends on whether or not you have enough room in your shop. I didn't. So I built one at a time. Either way, if you keep at it you'll get 'em both finished.
Having said that, there were a good number of smaller tasks along the way that I was able to do for both wings at once. There's definitely a significant amount of thinking, scratching your head, studying the drawings and figuring it all out as you go. Plus, setting up tools, jigs, and working methods. That all takes time. So whenever possible, I did smaller tasks for both wings as I went along so I wouldn't have to spend the time and energy, set up the tools, etc. a second time to do it again. You fabricate a part; do the second one for the other wing, too. That sort of thing. I deburred, fluted, and prepped ALL the ribs for both wings and tanks in one big batch. I just wanted to get it done and not have to come back to it. It made the second wing go together much quicker. It was a breeze that way. Hope this makes sense, and helps someone.