I successfully made my own flip folding device for t-shirts. It may not be glamorous, and it folds the shirt in a quasi-crooked fashion but twenty some wooden hangers were liberated from the closet in the process. The poorly cut lines of cardboard were covered up in ducted tape but the shirts will not know that when I use this nifty device.
The device was simple enough to make but if you are to try this on your own I would recommend using a thinner grade of cardboard. The one I used was very sturdy and made it tough to cut to precision, which lead to the shirts folding over in a crooked manner. If I had straight and proper lines on all three of the folding pieces I am sure this would not be an issue.
I also could not find a 72cm length of cardboard without a fold, or a bend in it but it did not affect the overall outcome. The most time consuming thing was cutting the pieces of cardboard, but that was partly due to the thickness of it. I would estimate about thirty minutes of effort went into constructing this and found that it worked pretty well.