Jane Wedlake, 54, suffered severe brain injuries after falling on to a hallway at the block of flats where she lived in November 2014.
She never regained consciousness and died in hospital 12 days later.
Cardiff Coroner's Court heard there were no warning signs in the St Mary Street property and residents could access the fourth floor atrium.
Jury members heard the whole building "shook" as she fell.
Ms Wedlake's partner Greg Capron said she may have been on the roof to retrieve washing that had fallen on to a glass roof.
He said losing his partner was "the worst thing that has ever happened in my life" and said he was left "totally traumatised".
Despite having keys to an access window, the inquest heard tenants were not supposed to enter the roof space of the flats owned by Cardiff Community Housing Association.
Officials said contractors only were supposed to use it.
Since Ms Wedlake's death, the window has been boarded up and large warning signs erected.
The jury returned a verdict of accidental death.
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