My advice: don't. Unless you have the correct tools, files, guages etc. I tried to cut my own and "eyeball" it against the one I was replacing and my guitar sounded like crap. Intonation was all over the map and tuning was a bee-otch. Caved in and had a graphite nut professionally installed along with a proper setup and it sounds absolutely awesome now. Intonation is dead on all over the fretboard (or at least as close as one can reasonably get it on a budget axe). Didn't think a nut would make as big a difference, but it did.
My 0.02. Oh, and it was cheap too. $40 installed and set up. Why bother with anything else?
Trev