i remember a similar thread to this when someone asked about 3 x 4oz vs 2 x 6oz. The generally consensus if I remember correctly was that you will use less resin by doing 3 x 4oz, achieveing a higher fiber to resin ratio and lighter laminate.
good luck filling the weave on 12oz glass…get ready for a really, really heavy board with little of the weight actually doing any useful reinforcing. Not saying it can’t be done, but 12oz? Yikes. I’ll be there are cheese graters out there that are smoother.
Personally, I’ve even sworn off of 6oz! 4 oz or less, multiple layers please.
Some of the older hands will attest to the fact that many board builders in the early 60s used single 20 oz glass jobs. I can’t imagine trying to work with that stuff.
I have an old issue of Surf Guide that lists who did this. Don’t have it handy at the moment. I’m on the road, so to speak.