I made a skull completly out of cardboard (just use cardboard boxes) and hot glue. If you want you can attach clay or something to it so it looks even more like a real human skull. I didn't make it, because I think it looks better like this.

Step 1: Construction

First I used 123D make from autodesk to design it. It's pretty easy to make but you can download it from here:

http://www.123dapp.com/make/skull/6178922

Step 2: Cut Out the Pieces

I printed the shapes out on paper and fixed them to cardboard.
Next I cut with a box cutter all layers out.

If you have a laser cutter it's much easier and not so time consuming.

Step 3: Glue It

Now you only have to glue the shapes together. Just use the instruction of the 123D make program. I glued it with hot glue but if you want you can use other glues, too.

Step 4: Enjoy

Now the only thing you have to do is enjoy the finshed skull or like I said in the beginning use clay for more detail and paint it if you want.

Thanks for reading this and have fun with making your cardbourd skull.

PS: Sorry for my english it's not the best.