The four men were working on the new extension at the premises in Brandon Court, Binley, Coventry on 26 June 2014.
One man was trapped by his legs, two suffered minor injuries and the fourth suffered severe grazing and a fracture to his lower spine.
The Worcestershire firm was prosecuted for safety failings following an investigation by the Health and Safety Executive (HSE).
Nuneaton Magistrates' Court heard that due to an omission during the planning and procurement process of the project, a critical structural truss had been overlooked.
This led to the workers attempting to install the truss in an unstable way, yet the employees stopped working in the area once they realised the issue.
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The following day however one of the trusses broke, creating a domino effect as several other trusses collapsed above the area the men were working.
The HSE investigation concluded had the work been properly planned, organised and monitored the incident would not have occurred.
If appropriate fall prevention measures had been implemented correctly, the outcome would have been less severe.
DP Designs pleaded guilty to two offences, one breach of Regulation 25(1) of the Construction (Design and Management) Regulations 2007 and the other a breach of Regulation 6(3) of the Work at Height Regulations 2005.
HSE Inspector Chris Gregory said: "As the principal contractor DP Designs Ltd should have ensured the roof truss installation was properly planned, appropriately supervised and, above all, safe.
"The company had a duty to inform those, who may be affected, of any changes to the plan that may impact on their work, in this case the company failed to inform workers of changes that led to the structure becoming unstable.
"Where work at height is involved, companies should also provide suitable measures to prevent falls and, secondly, provide equipment to mitigate the outcome of any falls. However, as a result of the DP Design Ltd’s failings, four men were injured."
(LM/CD)
