Billions of dollars of steel, glass and metal were no match for Mother Nature on Friday afternoon, when rain poured through the roof at the Oculus train station like a “shower overhead,” sending drenched commuters slipping and sliding for the door.

“You should have seen it! It looked like it was raining in here,” an employee mopping up puddles told The Post.

With a cost of $4 billion, the most expensive train station in the world somehow skimped on a proper roof, and Friday’s torrential downpour turned the World Trade Center shopping mall and transportation hub into a slippery mess.

“They had to shut down the escalators to make sure it didn’t cause a fire or anything . . . It’s a world-class building, everything’s supposed to be 100 percent,” the employee said.

Parts of the upper level near the Fulton Center exit were completely shut down around 4 p.m. with buckets and water vacuums in place. A Port Authority employee told The Post the station looked “like someone turned the shower on” and there was a “considerable amount of water.”

A retail employee at the shopping mall inside Oculus said leaking has happened at the station before. “I feel like we’re in the wild water kingdom, the Rainforest Café,” the employee joked.

Workers frantically redirected passers-by around the area where the flooding occurred, and the mess was still being cleaned after 5 p.m.

Jaylenne Guzman, 23, said it sounded like the storm moved indoors. “Between the two escalators there was a leak. It pretty much sounded like it was raining inside,” said Guzman, who works inside the Oculus.

Another employee said the leak was “only for a short while . . . maybe 10 minutes.”

The Port Authority said the situation is under control and “the leaks did not impact travelers going to and coming from PATH or NYC subways.”

“A substantial amount of rain today, coupled with several sections of the WTC site that are still under construction . . . caused water leaks in a few sections of the WTC Transportation Hub,” said the PA.

“World Trade Center staff has identified the specific areas where the leaks occurred and will take steps to mitigate future problems.”

This isn’t the Oculus’ first time dealing with rogue ceiling drippings — a persistent water leak was actually one of the main culprits behind the transportation wonder’s delayed opening, according to The New York Times.

The five boroughs turned into a mini-Atlantis on Friday afternoon when 3 inches of rain slammed Central Park in just three hours, AccuWeather senior meteorologist Dave Dombek told The Post.

Scores of New Yorkers waded through knee-length water, desperately puddle-jumped and cowered behind spiny umbrellas.