A man has fought back tears as he testified in Western Australia's Supreme Court how his friend repeatedly refused to get off the roof of his moving car before falling and suffering fatal injuries.

Jake Clinton Formica, 24, is facing a hearing over the death of James Della, 23, in Morley in August 2014.

Witnesses told the court they saw a car driving on the streets of Morley with a shirtless person on the roof "lying on his stomach ... with his hands stretched out".

One witness who was outside his home smoking a cigarette described what he saw as being "like the movie Titanic, the king of the world scenario".

He said he could hear people yelling like they were enjoying themselves.

In his evidence Formica said his friend, who had been drinking beer, jumped on the roof when the car stopped at a red light.

He said he and his brother, who was a passenger in the vehicle, repeatedly yelled at Mr Della to get off, but he would not.

Formica told the court he then decided to drive off because he "was just trying to get the car home", however he and his brother continued trying to convince Mr Della to get down from the roof.

"If he'd wanted to, I would have got him off the roof. I would have stopped the car," he said.

Formica said after he turned into the driveway of his family's home he realised Mr Della was no longer on the roof, and he thought his friend was going to jump out of the car.

He said he panicked when Mr Della did not appear, got back in the car and retraced his journey.

"I saw Jamie lying on the road. I thought he was playing a prank ... when I realised he wasn't joking I started screaming," Formica told the court.

An ambulance was called and Mr Della was taken to hospital where he died two days later.

Formica has pleaded guilty to a charge of dangerous driving causing death, but he is disputing some of the facts being alleged by the prosecution.