How to find user databases files size with script

Disk Space Used for all databases:

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;WITH DataBase_Size (SqlServerInstance,DatabaseName,DatabaseSize,LogSize,TotalSize)

AS

-- Define the CTE query.

(

  SELECT      @@SERVERNAME SqlServerInstance,

            db.name AS DatabaseName,

            SUM(CASE WHEN af.groupid = 0 THEN 0 ELSE af.size / 128.0E END) AS DatabaseSize,

            SUM(CASE WHEN af.groupid = 0 THEN af.size / 128.0E ELSE 0 END) AS LogSize,

            SUM(af.size / 128.0E) AS TotalSize

FROM        master..sysdatabases AS db

INNER JOIN  master..sysaltfiles AS af ON af.[dbid] = db.[dbid]

WHERE       db.name NOT IN ('distribution', 'Resource', 'master', 'tempdb', 'model', 'msdb') -- System databases

            AND db.name NOT IN ('Northwind', 'pubs', 'AdventureWorks', 'AdventureWorksDW')   -- Sample databases

GROUP BY    db.name 

)

-- Define the outer query referencing the  name.

SELECT *FROM DataBase_Size order by TotalSize desc