The phrase "are often large" is correct and usable in written English.
It can be used to describe the typical size of something in a general context.
Example: "The trees in this forest are often large, providing ample shade for visitors."
Alternatives: "tend to be big" or "are frequently substantial".
Brick ovens suitable to the task are often large enough to require municipal building permits.
Among the eastern Ijo, shrines for the water spirits have figures that are often large, though frequently kept hidden.
These candidate regions, called loci by geneticists, are often large and may contain many genes, any one of which could hold the suspect mutation.
Doig immediately agreed, with the proviso that Walcott, who had only seen small reproductions of his paintings, which are often large, should see them in person.
Strong safeties, who must force the run, are often large, but for a free safety, Tatum was an unprecedented physical specimen.
Her latest works are often large paintings on paper that depict animals in the wild, as freshly killed game or as taxidermied trophies sharing walls with various artworks.
Converted hotels are often large, have more bathrooms than comparably-sized homes and may even have eccentric features, such as ballrooms or grand entrances.
Airports are often large, labyrinthine spaces in which thousands of people need to be guided to particular places at specific times.
Low-tax companies are often large, global companies with the ability to use accounting maneuvers to shift earnings around the world.
In addition, executives, who are often large shareholders, stand to benefit from even a small, short-term jump in stock prices.
These problems are often large in size and known to be NP-hard to solve.
