You can choose whether members can create repositories in your organization. If you allow members to create repositories, you can choose which types of repositories members can create. Organization owners can always create any type of repository.
Enterprise owners can restrict the options you have available for your organization's repository creation policy. For more information, see "Enforcing repository management policies in your enterprise."
Warning: This setting only restricts the visibility options available when repositories are created and does not restrict the ability to change repository visibility at a later time. For more information about restricting changes to existing repositories' visibilities, see "Restricting repository visibility changes in your organization."
In the top right corner of GitHub.com, click your profile photo, then click Your organizations.
Next to the organization, click Settings.
In the "Access" section of the sidebar, click Member privileges.
Under "Repository creation", select one or more options.
Note: To restrict members to creating private repositories only, your organization must use GitHub Enterprise Cloud. For more information about how you can try GitHub Enterprise Cloud for free, see "Setting up a trial of GitHub Enterprise Cloud."