Pitch shifters that work on octave functions (ie up or down an octave) are fairly simple to achieve. Look for things like the MXR blue box, a couple of Dan Armstrong boxes (cant remember names off hand, but there's deffo an octave up one).
Schematics for some of the older boss oxtavers are available from various places online.
Anything further than straight octaves is a little more difficult. And to be honest, its probably cheaper to buy one of the behringer pitch shifters (they're not bad actually!).
S