I used leftover fabric from a pair of trousers, and I ransacked an old pencil case for the plastic. I didn't use exact measurements. I did most of it by eye, so it's a bit wonky, but the potential for making something really professional-looking is there, if you take more care than I did. It was also my first project of this nature. I only things I've ever made before is a pair of curtains, and a cosmetic case with a zip.
What you need:
~ very basic sewing skills
~ a sewing machine
~ standard sewing notions, like thread, scissors, pins, etc.
~ fabric, the amount dependant on size of project.
~ bias tape or fabric for the edges, or anything to decorate it.
~ plastic for the games slots, if you want, but can use fabric.
~ Depending on size, detail, and skill, about 6 hours/weekend?
~ a presser foot that will work with plastic