I tried doing that for a project. The way I did it was by measuring the width at the nut and at the end of the last fret, the depth of the neck at its deepest point (radius), the distance between the nut and the bridge (for fret calculations), the fretboard length and the depth of the neck joint. You'd have to cut the bottom of that to fit into what ever guitar body you have though. Make sure you measure it specifically.