This is much better than using giant buttons which have very limited visibility.
My friend claims he had perfect vision out of his button eyes, while mine minimally hurt my vision (the prescription lenses had different clarity depending on what angle I was looking out of them).
Step 1: Materials
If making non prescription lenses, either use plexiglass or you could potentially find pre-cut glass circles (used in photography I think).
Dremel tool with a sand grinder
Black Model Magic air dry clay by Crayola
soapy water (should be in a spray bottle, but I just dabbed it on)
Exacto knife or box cutter
Circle cutter or compass
Hole punch (1/8'' hole)
Limo tint - can be bought in huge rolls, but you possibly could find some scraps at a place that tints windows or on ebay. Or PM me. I have a huge roll and I could potentially ship you some if you pay for shipping.