"sizeable role" is correct and can be used in written English.
You can use it to describe a significant or influential role. For example, "My manager played a sizeable role in helping me develop my career."
The only requirement is that each opera include a sizeable role for chorus.
Brotherhood members played a sizeable role in Tahrir – but at the time, even Morsi claimed the group had little interest in power.
The Dragon capsule is capable of supporting a human crew of up to seven astronauts; if the tests are successful, Space X look set to play a sizeable role in the future of human space flight.
Shot on his home turf in Portland, Oregon, it focuses almost exclusively on two school-age protagonists: Enoch, played by Henry "son of Dennis" Hopper in his first sizeable role, and Annabel, played by the somewhat more established Mia Wasikowska.
It's also a pleasure to see Allen in a sizeable role again in an enjoyable cast that includes Cate Blanchett as a Soviet superagent, Ray Winstone as a double-, triple- or quite possibly quadruple-agent and John Hurt as a sort of 1950s Ben Gunn.
Diffusion mechanisms play a sizeable role.
Her political views, like Mr Kirchner's, were forged in the Peronist left of the 1970s: nationalism, a sizeable state role in the economy and hostility to the armed forces.
But the Territorial Army TAA) - in the process of being rebranded the Army Reserve - already makes up a sizeable part of the British Army's manpower and will soon be playing an even greater role.
As Dano began appearing in small roles on TV – he was in a few episodes of The Sopranos, a single episode of the sitcom Smart Guy and, at the age of 17, won a sizeable part in the movie L.I.E.
Another sizeable part provides for differences in niche exploitation.
Plaudits too to Gérard Depardieu, who sinks his sizeable teeth into the role of old flame Maurice Babin, and to Fabrice Luchini, who makes a fine fist of tyrannical boss and unfaithful husband Robert.
