Flat roof for brownstone - opinions on SBS vs APP

Looking for a second opinion / validation of my roofer’s initial recommendations. Any views on APP vs SBS modified bitumen – from my web browsing, it appears that both are fine, and APP a bit better to work with during installation. In addition, we will be looking to use pavers on pedestals in one area of the roof – is an additional protective board below the pedestals an optional extra level of protection, or an essential element?