I looked at my drive if I had a Poliigon material and found one. I think it’s like this:
I don’t have a preview from this one but it looks quite like rusty metal, I used the Generic material since that has all you need I think
COL: base color of the material
GLOS: is the opposite of roughness, so tie to roughness and add an invert node
REFL: the specular amount
NRM: bump map
DISP: a lower resolution displacement map
DISP16: is a16-bit displacement map you tie to a geometry node
With PBR textures a material is basically either a metal or not a metal. So everything in between is non-existent in real life. Metal with a layer of paint is a non-metal for example. So if you have a METALLIC map it’s most of the time a black/white image. For example, if it’s damaged painted metal the parts where you see the bare metal would be white in the METALNESS image.
As you see here I just put a ‘1’ in the Metallic value since it might be rusty, it’s still a metal (right side of screenshot).
Some things to consider:
Depending on your material it’s not always needed to add the displacement map. A displacement map will create more geometry and cause longer render times and takes more (V)RAM to render. For example: I would never use it if it’s only a scratched material but if the material has some kind of structure and you do closeups you can use it for a more realistic view.
The DISP16 is a 16-bit displacement map and if I’m correct they get internally translated to 32-bit and will cause more memory to be used. The DISP is just a 8-bit image which will use less (V)RAM but because of the compression (I’ve a JPG here) also cause a bit of disturbed geometry. I think that if your scene has enough with the 8-bit you could consider to not use displacement at all.
Maybe others have something to add but this is as far my knowledge goes 
