Cardboard seems to be the material of choice to make a Transformers costume. It makes sense given that cardboard is relatively inexpensive (or free), easy to find, and lightweight. Instructables user operationremie turned to the material for his Grimlock costume; he only had to add Krylon spray paint. He used online tutorials and a Grimlock action figure as inspiration:
I figured cardboard would be the best option to go with for my first one since it was very durable when combined with each other. So the quest began with cardboard and hot glue. The most challenging part of this whole costume was the lack of patterns available. I began with the head/helmet. It involved a hard hat and lots of cardboard. I started making a pattern for most of it out of paper but found out that it was very difficult to actually get the actual pattern to work. So I just started cutting cardboard pieces out and putting it all together using scotch tape until it started holding enough for me to glue it together. Once the entire head was made, I went and bought a blue see-through rubbermaid container to use for the eyes/visor so I could actually see out of it.
After that, it was pretty much “Let’s build each part and spend a few months doing it” time. I took a medium size cardboard box and used it as the upper body. I put a backpack inside of the back so everything would be sitting on my shoulders instead of just floating there. The dinosaur head on the back would cover the entire thing so no one would be able to really see what was holding things on there. I just cut most things out and looked to see if they worked. If not, I would go and re-cut them until they did. It was a lot of trial-and-error on my part since I had never done anything this big before.
Read more at Instructables.