Context Clues

Construction on Florence's grand cathedral began in 1296. Over a hundred years later, however, the structure remained unfinished , with an enormous hole in the roof. The designers had intended to top the cathedral with the world's largest dome, but this plan was stymied by architectural limitations. The main factor stalling progress was the fact that no one knew how to create such a massive cupola without large , cumbersome support systems. 

I think the meaning of cupola is dome because in the text it says it was supposed to be the world,s largest dome. 

Why I don't think cupola means roof. Is because it says there is a massive hole in the roof but it's supposed to be a dome not a roof.

It's not supposed to be a decoration it's supposed to be a cathedral.

They wanted to make the worlds largest dome but they already made the cathedral.