As permissões são herdadas do início , nesse caso, da organização :
By default, when the organization is created your entire domain is granted Project Creator and Billing Account Creator IAM roles at the organization level. This ensures that users in your domain will be able to continue creating projects as they did before and no disruption occurs.
The Organization Administrator will decide when they want to start actively using the organization. They can then change the default permissions and enforce more restrictive policies as needed.
Em Usando a hierarquia de recursos para controle de acesso , há uma preciosidade no final:
If you want to limit project creation in your Organization, change the Organization access policy to grant the Project Creator role to a group that you manage.
Especificamente, a função que você deseja deserdar é roles / resourcemanager.projectCreator :
Provides access to create new projects. Once a user creates a project, they're automatically granted the owner role for that project.