CREATE DATABASE permission denied in database 'master'. unable to get the permission
The user must be a member of dbcreator server role for user to have enough permissions to create a database. 

You can execute the following statement to make a user member of dbcreator server role.

EXEC master..sp_addsrvrolemember @loginame = N'Shubhankar', @rolename = N'dbcreator'
GO


Members of sysadmin role are by default members of dbcreator server role therefore they can create databases too.