Estoy tratando de implementar el código de este repositorio:

https: //github.com/anishkny/puppeteer-on-cloud-function

en Google Cloud Build. El contenido de mi archivo cloudbuild.yaml es:

steps:
- name: 'gcr.io/cloud-builders/gcloud'
  args: ['beta', 'functions', 'deploy', 'screenshot', '--trigger-http', '--runtime', 'nodejs8', '--memory', '1024MB']

He asignado los siguientes roles a mi cuenta de Cloud Build Service (**** @ cloudbuild.gserviceaccount.com):

Sin embargo, en mi registro de Cloud Build veo el siguiente error:

starting build "1f04522c-fe60-4a25-a4a8-d70e496e2821"

FETCHSOURCE
Fetching storage object: gs://628906418368.cloudbuild-source.googleusercontent.com/94762cc396ed1bb46e8c5dbfa3fa42550140c2eb-b3cfa476-cb21-45ba-849c-c28423982a0f.tar.gz#1534532794239047
Copying gs://628906418368.cloudbuild-source.googleusercontent.com/94762cc396ed1bb46e8c5dbfa3fa42550140c2eb-b3cfa476-cb21-45ba-849c-c28423982a0f.tar.gz#1534532794239047...
/ [0 files][    0.0 B/  835.0 B]                                                
/ [1 files][  835.0 B/  835.0 B]                                                
Operation completed over 1 objects/835.0 B.                                      
tar: Substituting `.' for empty member name
BUILD
Already have image (with digest): gcr.io/cloud-builders/gcloud
ERROR: (gcloud.beta.functions.deploy) ResponseError: status=[403], code=[Forbidden], message=[The caller does not have permission]
ERROR
ERROR: build step 0 "gcr.io/cloud-builders/gcloud" failed: exit status 1

¿Qué me estoy perdiendo