Updated for dynamic variables

Modified slightly for dynamic variables, so that you can input a volumename instead, and specific a warning / critical –
Comment out the previous Critical / Warning variables or replace them with below –

#Modified for dynamic variables
#use as script.ps1 volumename warningvalue critcalvalue
$Volumename = $args[0]
$Critical = $args[2]
$Warning = $args[1]

Replace this line –
$volumes = Get-WmiObject -computer $server win32_volume | Where-object {$_.Label -eq $Volumename} | ForEach-Object {

Add args to your nsclient.ini –
check_windows_volume_mount_point_freespace_custom=cmd /c echo scriptsCheckWindowsVolumeMountPointFreeSpaceCustom.ps1 $ARG1$ $ARG2$ $ARG3$; exit($lastexitcode) | PowerShell.exe -Command –