Clark Brothers Limited was carrying out refurbishment work at 10-12 High Street Bilston in June last year when the floor collapsed, sending Ian and Jamie Colbourn, from Penkridge, plummeting to the ground.
Wolverhampton Magistrates' Court heard how Jamie Colbourn, 20, had to dig his father out of the rubble. They had been hired to carry out brick work at the building.
The court was also told that Mr Colbourn Snr, 51, had warned his son about the safety of the building after seeing the wall move.
Mr Paul Cooper, who was prosecuting on behalf of the Health and Safety Executive, HSE, said it was a 'miracle' that no-one was killed.
Mr Cooper told magistrates that the Birmingham-based Clark Brothers Ltd hadn't carried out the necessary safety checks on the property before they recruited a number of traders to go on site and renovate the property.
He said: "A conscientious developer would check the competency of any contractor on site.
"Tony Clark, a director of the firm, had no qualifications or training and assessment of the property was carried out.
"It should have done because no contractor or member of the public would have been at risk.
"The contractors should have been briefed by someone at the company with the relevant health and safety training or they should have employed someone with the required qualifications."
It is not definitive what led the floor to collapse but the HSE said that a number of building blocks stored on the second floor could have weakened the structure when the Colbourns went to carry out the work.
The men were taken to hospital for their injuries and the building was sealed off while an investigation was carried out.
HSE inspectors found that the refurbishment project was unsafe and immediately issued a prohibition notice stopping any further work at the site. Mr Harry Owen, representing Clark Brothers Ltd, said: "The building was no longer commercially viable to redevelop and sell for profit.
"They were left with a building they were going to make a loss on and their aim was to get it fit and safe and possibly sell it to the local authority.
"Mr Tony Clark wasn't trained and thought, much like if I had a contractor in my home, he would be responsible for any health and safety issues, but that wasn't case here."
Clark Brothers Limited pleaded guilty to a charge of employer/self-employed person breach general duty to other than employee.
Magistrates fined them £10,000 and they were ordered to pay the £1,844 costs of the HSE. They were also told to pay a £120.
Chair of the magistrates Mr Stephen Russell said during sentencing: "There was a risk to the public.
"I don't think anyone would have predicted which way the collapse could have fallen. People could have been killed."
Speaking after the hearing, Mr Cooper said: "Clark Brothers Ltd made a number of serious errors in attempting to undertake this work without proper planning, training and supervision.
"Their failure to manage this project placed workers and the public at serious risk.
"A floor collapse, as with any unplanned demolition work, presents very serious dangers that can result in serious or fatal injury.
"The fact the father and son escaped relatively unharmed in this collapse is remarkable.
"The uncontrolled collapse of the building also posed a risk to members of the public who were out on the high street that morning."
In April, Brownhills firm JSF Stainless Steel and its director Richard Lancaster had to pay out £23,000 in court costs and legal fees after 19-year-old Louis Parkes lost three fingers while cleaning a saw.
Mr Parkes, now aged 19, was just 17 when his left hand was slashed by a 21cm blade when he was removing metal shavings from a Sabre saw at JSF.
The teenager was working as a general labourer tasked with sweeping the floors and keeping the workshop clean when the accident happened in June 2011.
In June demolition and excavation company was fined £3,500 after a worker from West Bromwich trapped their arm in an unguarded crushing machine.
The 33-year-old plant operator from West Bromwich was hurt when his right arm was drawn in between the rollers and conveyor belt at Great Barr-based Coleman and Company's site in Meriden, Warwickshire. The worker suffered fractures to his right arm along with wrist injuries and bruising, and he needed several skin grafts.