I have used a one sided eps panel system almost exclusivly for 20+ years. 1 sheet osb laminated to 7 1/2" eps installed over 2x t&g. The few built up systems I have tried have been much more labor intensive. The built ups are also usally thicker and look boxier on the eaves. The bottom line may be the cost, if your timber framer says he will do a built up for less why argue?
