ok then, as philly says 3/8" will give you room for plenty of bevels and still have a bit of wood underneath.
if you have thinner wood for the top you can still get nice mean looking bevels by making them ever so slightly concave, recurved, carved out. Not so much that it looks over done or unlike an sg, but a little bit enhances the sharpness of the bevels a lot.
Imagine putting a straight edge on the bevel between the face of the guitar and the side of the guitar. if the centre of the bevel is 1mm lower than the edges it will sharpen the look of the bevels a lot but still look quite like a flat surface