Roah is a type of wood found all across the world of Temerant.
It is hard, heavy and impermeable to flame. It is however quite rare and expensive as it is "worth its weight in gold" and so far as we know may only be grown near Aryen, which is where Graham had the wood shipped from to build the mounting board for Kvothe's sword, Folly.
In the chronicle
It is mentioned that Roah smells of citrus, which leads us to assume that the Loeclos Box, Folly's mounting board and perhaps even the tree in which The Cthaeh lives are made of Roah wood since all are said to smell like "smoke and spice and leather and lemon"