Where does one place custom materials?

Hello,
I am working on a recreation of the Shadow Moses Island Heliport for Garry’s Mod/TTT , and I have the base map ready.
But I don’t know where precisely to place the textures for a static fence prop that I am going to use in Hammer, as the only tutorial I found on the subject uses an older directory that (I believe, CMIIW,) isn’t used for this anymore. (common\GarrysMod\garrysmod\materials)

Where do I place my prop materials?
Also,
Do I need to do anything special with my materials and models or place it somewhere different if I am going to include it in the map .bsp?

Sorry for the lengthy question.

if its going to be released as an addon then the easiest is:

common\GarrysMod\garrysmod\addons/<YOUR ADDON NAME>/materials/models/<PROP NAME>

or if its for a map texture:

common\GarrysMod\garrysmod\addons/<YOUR ADDON NAME>/materials/map/<TEXTURE NAME>