Here are a couple of modifications i did to a guitar i picked up second hand for 30 quid (found out later i could've bought the guitar new for 25....goddamn cheating guitar shop man)
Didn't really take enough build photos to warrant an instructable, so In no particular order here is a list of the modifications made:

Sound hole cut bigger and speaker mounted in place.
Holes cut in body for electronics and metal plate mounted over top
Sprayed guitar body blue
LM386 modified "little-gem" 1/2 watt amp mounted in body
Peizo mounted in bridge
Peizo buffer mounted on metal plate(modified version of this
Cut f-shaped sound hole (Little known fact: f-shaped sound holes make anything cool)
Sanded down the neck and head
Did some carving on the guitar head

Still got quite a bit to do but won't have time for a while so i thought i'd post this up now anyway. Planning on adding a jack socket so it can be plugged into an amp and a fuzz face and tremelo effect inside the guitars body and maybe a kill switch. Also need to add a battery box so its not powered off of a dangly wire.

Heres an extra bonus video of me in all my dashing glory talking about the guitar and playing it badly. Apologies for the horrendous out-of-sync-ness of the video .