This is akin to the personal wheel building question. Yeah, you can buy professionally built wheels and save yourself a lot of time and money. But for true cyclists I think it's a good experience to lace a wheel or two (which I've done) just to get an appreciation of what's going on down there. Maybe the same can be said for rebuilding a freewheel (which I have not done). But yeah...I'd buy a new freewheel before attempting a rebuild of one.

Dan