It depends what you want to build. If it's a Strat or Tele type, Allparts sell decent bits. However, it's still likely to cost you more than buying a ready assembled guitar, and the resale value is likely to be low - buyers like known brand names.
If you buy the various bits on eBay you could save lots of money. All the bits of this (apart from the new scratchplate, pots, switch etc.) were bought from eBay and assembled by me:
The Warmoth ash hardtail body cost me ?165, the Fender CIJ 62RI neck was around ?200 with tuners. All in all, it cost me about ?500, but I doubt if I would get that if I tried to sell it. It was very satisfying to build it all myself, & it taught me a lot, but the neck still isn't right - it's too chunky for me.
Beware though, there are even more dodgy parts on eBay than there are dodgy guitars - "solid" Strat bodies that are either ply or balsa! "Fender" necks that are Squier necks with a new decal. And then sometimes a neck and body just won't match up - it can be a bit of a lottery. Buying second-hand pickups seems to be a safer bet though.
Hope this helps.
Mike
