Mine is a War Machine (Iron Man) helmet I started making a few years back out of paper. It's called pepakura which apparently means paper craft/model. You basically take a 3D model of something and export it down to a flat constructable paper (and tabs) which you can then cut out and build into your own model. The more detail you want, the more complicated it gets (i.e. more pieces and more gluing). It took me 9+ hours just to cut out all the pieces. After that, I glued it all together (used a hot glue gun) which took quite some time, as well. I put one coat of epoxy on it to harden it up a bit and that's where I stopped. I always tell myself I need to finish it, but never have the time to do it. So, it sits in my garage waiting for me to be motivated and confident enough to finish it and dare to wear it at Comic-Con.