How can I make these?

sheet of wood about 1/2 inch or 1/4th inch would probobly be the easiest to do without much experience.

You trace your design on the wood then cut it, then you can paint it red and so forth :)

Here is a how to you might find useful: http://www.ehow.com/how_6939118_cut-out-wood-patte...

Should be able to get everything you need at a hardware store.

Also there might be a way to do it if you find a stiff foam sheet, then cut it out of the foam , that would be alot easier but harder to find the foam sheet stiff enough.

Vist a hobby store or a craft store and ask the sales person if they have foam sheets and then you can look to see if they have anything stiff enough.

Good luck with your cosplay!

Edit:

I forgot something

styrofoam sheets would also work and be fairly easy.

Again, good luck.