We have installed large roof tiles that have one inch thermapole in them, tile is about three inch thick. it is good, it can handle weight of water tank of 500 galons and does not leak.
if you just use normal thermapole sheet, it will compress due to the weight and then its not going to stop the heat at all. An expert told me that jumbolon handles weight and is leak proof and has a long life. next house we build we will use 3 inch jumbolon topped with 2 inch sand and final 2 inch layer of concrete mix