Why rebuild?
As other have said, its far cheaper than buying really crappy, useless, worthless, stock coils.
Also, a rebuilt is not crappy, useless or worthless

.
Rebuilt coils have far superior flavor, much cleaner vapor and resistance for resistance they produce much more vapor as well.
My favored build:
1/16th inch internal diameter, on either a precision screwdriver or drill bit.
30 gauge wire
8 wrap contact coil (aka micro coil)
1 strand of peaches n cream ekru cotton yarn through the center
This build comes out to 1.8 ohms, and never leaks.
PS. With the frequency that I post that build setup.. I really need to write a guide/blog post about them.