i'm going to start a new project by building a les paul but i want to build a couple of effects into the guitar. A Boss FZ-5 & a Boss AW3.

Does anyone know how it is done?, how to power them? how to wire it all up?

You just wire a pedal in before the output jack on the guitar,

you will most likely to need to do some routing to fit the boards inside.
They are powered by batteries, so easy access will need to be established.

*edit* just realised that my post wasn't really that helpful*
In essence, your removing the jack from the guitar, and the input jack of the pedal, and connecting them. Then just using the output jack of the pedal as the output for the guitar. Its fairly simple, just make sure there's enough room, and you can get to your battery easy enough
you wont get 2 boss pedals in a LP without serious routing
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Put in a delay that lets you oscillate the pitch by changing delay speed... That would be awesome onboard a guitar.

Good luck making this look attractive, or at least practical.
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the wiring would consist of taken off the output wire to the guitar jack, and attach that to the input of the pedal. You will also probably wanna change your jack to a stereo jack, and connect the negative of this to the sleeve I believe, so it will only drain the battery when a cable it plugged in. Also make sure that the ground from the input cable is also attached to the same ground as the rest of your guitar I.E either directly to the output jack, or on top of a pot, etc...)

You will also probably want to take off the LED, it would be kinda unnecessary and would just drain more of the battery. You could also rig a push pull pot or something, or just add a switch to turn it off and on
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look at how the onboard effects are wired on gutiarfetish.com they sell all kinds and have instructions/diagrams, just dig around there a little bit, should help some at least.
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