what prep do i need to do with building a guitar body?
i have all parts and the neck all ready, but so far my body is a big block of mahogany and thats it! i really dont want to mess it up so please tell me what i can do so that doesnt happen!!
Have you got a template of the body cavities? Stew-Mac has several different templates. How are you planning on cutting the body?

4 Custom Strats
1 Custom Soloist (Warmoth)
1 Custom Telecaster (Warmoth)
2007 Jimmie Vaughan Sig Strat

Callaham Hardware & Bridges
Fender Custom Shop 69's
Dimarzio Breed Pickups

Blues Junior Amp
BlackStar HT Club 40 Amp
thats a really general question man...

we don't know what body shape you're doing, if theres a carve, how much routing needs to be done, what kind of bridge you're using, what kind of pickups, what sort of control layout, what kind of tools you have access to, or..any of that stuff.

You'll want to get the shape you want drawn out on the blank. There are several different ways to go about that, template, tracing a body, free handing etc.

For cutting a Mahogany blank I recommend using a bandsaw with a good sharp blade. Stay on the outside of your line to allow you some room for sanding.

You'll need a router to route the neck pocket, pickup cavities and control cavity. Its helpful to make templates to guide the router.

Theres a link to my newest build in my sig, where you can see the process of turning a Mahogany blank into a body.
I'm using Les Paul Parts that i ordered in a kit. my father and i were thinking of using the router to cut it out, and if not, somehow getting a band saw.
the shape is my own design, kind of a Les Paul/Strat/flying V hybrid thing. but the controls together like a SG.
at the moment the outline is traced on but the neck pocket isnt done well.
ive no template for anything but the outline since i dont know measurements or anything for cavities