I bought 2 of the shirt below and cut the second one up to do both of the gray shirts, I didn't really have a tutorial for them I just got ideas from everywhere else. I hand sewed the one above, it took a really long time but it was worth it.
I learned a few things on this one. Here is some tips to help you out. FIRST, try on the shirt to mark the EXACT middle. SECOND, iron the strips into the folds, then pin (or even better baste) them to the shirt before sewing, i just used lots of pins but one of them might still be slightly crooked. Its hard to tell though. If you make some let me know!!