"Based off a dream I had, the creatures were large (100ft-300ft) and hostile to any and all life they encountered and seemed to be made of a concrete like material that took very little damage when hit.

No idea what they are called but there was more than one of them, I would say 8 in a 6 mile radius of the empty barn me and the survivors were hiding in.

We just call them "Concrete Crawlers".

Despite having no eyes or face, they can see, smell and hear extremely well, they can even reach into buildings, windows, etc; Grabbing people with ease.

Their presence often is given away by a distinct "silence" that seems to follow them, the creatures themselves making strange chopping, shuddering clicking that echoes through the empty streets.

The air and sky also seems to become contaminated over time by some sort of agent they naturally release.

This agent caused the following effects after prolonged or intense exposure:

Rash and Intense Itching.
Dry Cough.
Runny Nose in Some Cases.
Hallucinations.
Delirium.
Madness in Some Cases.
Mania in Some Cases.
Aggression in Rare Cases.
Increased Hunger.
Headaches.
Nightmares.
Nausea.
Cysts in Some Cases.
Coma, Seizures or Brain Death if exposed to large quantities or for prolonged periods.

The origins of the Concrete Crawler is unknown, but they are theorised to be an extradimensional creature or biological weapon of some kind."