Beanie Feldstein broke out as Saoirse Ronan’s BFF in “Lady Bird” and now the supporting actress is getting her own film. She’s signed on to topline a film adaptation of Caitlin Moran’s “How to Build a Girl,” Deadline confirms. Protagonist is launching world sales in Cannes.

Published in 2014, Moran’s coming-of-age novel is set in 1990 and centers on 16-year-old Johanna Morrigan. Determined to leave her hometown behind, Johanna reinvents herself as music critic Dolly Wilde. She’s simultaneously dealing with deadlines, raging hormones, body image issues, and annoying siblings.

BAFTA nominee Coky Giedroyc (“Harlots,” “The Hour”) will direct the pic.

Monumental Pictures developed “How to Build a Girl” with Film4. Alison Owen (“Me Before You”) and Debra Hayward (“Bridget Jones’s Baby”) are producing.

“We could not be more excited for Johanna Morrigan to burst onto the big screen,” said Owen. ” We searched high and low for a girl who could match the boundless wit, sparkle, and big heart of Caitlin’s super-heroine and feel incredibly lucky to have found her in the effervescent Beanie Feldstein.”

Hayward added, “’How to Build a Girl’ will be outrageously funny and utterly affecting, even heart-breaking. With Coky Giedroyc at the helm of Caitlin’s swashbuckling script, we are blessed to have a director who can deliver all this in spades.”

Besides her best known role in “Lady Bird,” Feldstein’s screen credits include “Neighbors 2: Sorority Rising” and Whitney Cummings’ ensemble comedy “The Female Brain.” She recently made her Broadway debut in “Hello, Dolly!”

Feldstein is signed on to star alongside Kaitlyn Dever (“Last Man Standing”) in “Booksmart,” Olivia Wilde’s feature directorial debut. The pic follows overachieving BFFs who have an epiphany on the eve of their high school graduation: They realize that they should have spent less time studying and more time partying. Determined to catch up to their peers, the girls try to cram four years of fun into one night.