Don't get too hung up on the tool names. Think of them in terms of what they do and how they work then use the most appropriate tool to your conditions. In this case, the mesh tool would be the best choice, although I would certainly consider using multiple elements, such as a slab or roof for the decking and mesh for insulation above, to more closely relate to how the roof would be constructed in reality.
Erich
AC 19 6006 & AC 20
Mac OS 10.11.5
15" Retina MacBook Pro 2.6
27" iMac Retina 5K