Full Code

SELECT
   SUBSTRING(a.FILENAME, 1, 1) Drive,
   [FILE_SIZE_MB] = convert(decimal(12, 2), round(a.size / 128.000, 2)),
   [SPACE_USED_MB] = convert(decimal(12, 2), round(fileproperty(a.name, 'SpaceUsed') / 128.000, 2)),
   [FREE_SPACE_MB] = convert(decimal(12, 2), round((a.size - fileproperty(a.name, 'SpaceUsed')) / 128.000, 2)),
   [FREE_SPACE_ % ] = convert(decimal(12, 2), 
   (
      convert(decimal(12, 2), round((a.size - fileproperty(a.name, 'SpaceUsed')) / 128.000, 2)) / convert(decimal(12, 2), round(a.size / 128.000, 2)) * 100
   )
),
   a.NAME,
   a.FILENAME 
FROM
   dbo.sysfiles a 
ORDER BY
   Drive,
   [Name]

Full Code

SELECT
 SUBSTRING(a.FILENAME, 1, 1) Drive,
 [FILE_SIZE_MB] = convert(decimal(12,2),
round(a.size/128.000,2)),
 [SPACE_USED_MB] = convert(decimal(12,2),
round(fileproperty(a.name,'SpaceUsed')/128.000,2)),
 [FREE_SPACE_MB] = convert(decimal(12,2),
round((a.size-fileproperty(a.name,'SpaceUsed'))/128.000,2)) ,
 [FREE_SPACE_%] = convert(decimal(12,2),
(convert(decimal(12,2),round((a.size-fileproperty(a.name,'SpaceUsed'))/128.000,2)) 
/ convert(decimal(12,2),round(a.size/128.000,2)) * 100)),
 a.NAME, a.FILENAME
FROM dbo.sysfiles a
ORDER BY Drive, [Name]