You dont want to know why??? Plywood is terrible. it is not a true wood, it may be extremely strong for other applications but not up to par for guitarbuilding. I suggest you do some thinking about what type of sound you want from your guitar. Do you want it to be mellow, deep, sharp or what? then start to search google for compatible wood types. Or indeed ask here. But plywood is NOT the way to go!
Good luck mate