Can Billing Account User or Project Billing Manager create billing account?? As per my understanding User can link project to billing account but can't unlink. whereas manager can link and unlink project to/from billing account.
Can Billing Account User or Project Billing Manager create billing account?
No exactly. Let me give you some insights on how Billing roles works on Google Cloud.
The main question that you have to ask yourself is: my project is inside an Organization node or not?
To check if your project is inside an organization, you could take a look at this piece of documentation where it talks about retrieving your organization's ID.
To sum up, you could spin up the Cloud Shell and run the following command in order to see all your organization's ID if you have any:
gcloud organizations list
This will list all the organizations to which you belong to, and their corresponding organization IDs.
If you are not a member of a Google Cloud Organization but instead are managing your Google Cloud resources or Google Maps Platform APIs using projects, you do not need any specific role or permission to create a Cloud Billing Account, as stated here.
If you would like to create a new Cloud Billing Account and you manage your Google Cloud resources using an Organization node, and you are a member of that Google Cloud Organization, then you must be a Billing Account Creator to create a new Cloud Billing Account.
As stated here:
Use Billing Account Creator's role for initial billing setup or to allow creation of additional billing accounts. Users must have this role to sign up for Google Cloud with a credit card using their corporate identity.
A nice tip is to minimize the number of users who have this role to help prevent proliferation of untracked cloud spend in your organization or project.
Project Billing Manager Vs Billing Account User
You basically nailed it, but if you would like to have further information, you can refer here for a more detail explanation, but I will resume it below:
Project Billing Manager is the role in charge of link/unlink the project to/from a billing account as you well said.
This role allows a user to attach the project to the billing account, but does not grant any rights over resources.
As for Billing Account User, the role allows to link projects to billing accounts.
This role allow a user to create new projects linked to the billing account on which the role is granted.
Finally, I attached you some documentation regarding: