piece of advice about the wood.
you can either go to home depot and get pine or poplar or the like for about 20.... and it will LOOK like you made it out of pine. or you could get on ebay, and find some mahogany, alder, swamp ash, lightly figured maple, ect. and pay 20-50$ for it and have a NICE looking body.
so, its up to you. but i went for about 250$ for my first guitars wood. and its going just fine. glad i didnt screw around with some cheap wood. just take your time and you wont mess it up.
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you can either do a flat top or a carved top. usually on carved tops its a seperate piece of higher grade wood.
of course it will take more time, skill to do any carving but it depends on you if you think you can do it.
if you decide to do a carved top you'll have to compensate that height of carving in the purchase of your wood, or buy another piece and glue it to your body and carve from that.
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for me i always work from a center line. to me it's easier to keep track of the measurement and you normally never cut away your reference lines. helps when the object your working with is symetrical like a guitar, instead of a freeform sculpture or something.