Ok this is kinda simple, for the most part your going to be layering ducttape. First grab some old news paper, a dark colored marker, scissors, a shirt that fits you well, and a ton of duct tape.
Fold the shirt in half (hot dog) and tuck in the sleeves to the inside until you get to the seams.
Then place the folded shirt onto the news paper and make an outline of it X2.
Now, unfold your shirt, but keep the sleeves in and draw the outline on another sheet of newspaper.
Now you have the pattern.
This part will probably give you some trouble, but next make long strands of duct tape, folding them over so sticky side with sticky side and long enough to be able to fit the pattern. Once you have enough strands your going to over lap the duct tape with more duct tape. Kinda like a criss-cross pattern.
Once you have enough to cover the pattern, place the pattern over the duct tape and outline all three pieces (separately ). Then cut them out.
Now all you have to do is put all the parts together with more duct tape, remember not to duct tape together the sleeve holes.
Also you have the option of cutting the neck area or simply folding it over.
If you choose to fold it try to keep an elephant clip on it for a while so it stays once you take off the clip.
If you choose to cut it make sure to add duct tape on that area so its smooth and not jagged or sticky.
Once its all together you can decor it as you will, by adding pockets or some kind of pattern/stencil and you can also add buttons.