Get size of folder

Get-FolderSize.ps1

Function Get-FolderSize {
    [cmdletbinding()]
    param
    (
        [Parameter(Mandatory = $false)]
        [Alias('Path')]
        [String[]]
        $BasePath = 'C:\',        
        [Parameter(Mandatory = $false)]
        [Alias('User')]
        [String[]]
        $FolderName = 'all',
        [Parameter()]
        [String[]]
        $OmitFolders,
        [Parameter()]
        [Switch]
        $AddTotal
    )
    if ($folderName -eq 'all') {$allFolders = Get-ChildItem $BasePath -Directory -Force | Where-Object {$_.FullName -notin $OmitFolders}}
    else {$allFolders = Get-ChildItem $basePath -Directory -Force | Where-Object {($_.BaseName -like $FolderName) -and ($_.FullName -notin $OmitFolders)}}
    [System.Collections.ArrayList]$folderList = @()
    ForEach ($folder in $allFolders) {
        $fullPath = $null        
        $folderObject = $null
        $folderSize = $null
        $folderSizeInMB = $null
        $folderSizeInGB = $null
        $folderBaseName = $null
        $fullPath = $folder.FullName
        $folderBaseName = $folder.BaseName
        $folderSize = Get-Childitem -Path $fullPath -Recurse -Force -ErrorAction SilentlyContinue | Measure-Object -Property Length -Sum -ErrorAction SilentlyContinue       
        $folderSizeInMB = "{0:N2}" -f ($folderSize.Sum / 1MB)
        $folderSizeInGB = "{0:N2}" -f ($folderSize.Sum / 1GB)
        $folderObject = [PSCustomObject]@{
            FolderName    = $folderBaseName
            'Size(Bytes)' = $folderSize.Sum
            'Size(MB)'    = $folderSizeInMB
            'Size(GB)'    = $folderSizeInGB
        }                        
        $folderList.Add($folderObject) | Out-Null
    }
    if ($AddTotal) {
        $grandTotal = $null
        if ($folderList.Count -gt 1) {
            $folderList | ForEach-Object {$grandTotal += $_.'Size(Bytes)'}
            $totalFolderSizeInMB = "{0:N2}" -f ($grandTotal / 1MB)
            $totalFolderSizeInGB = "{0:N2}" -f ($grandTotal / 1GB)
            $folderObject = [PSCustomObject]@{
                FolderName    = 'GrandTotal'
                'Size(Bytes)' = $grandTotal
                'Size(MB)'    = $totalFolderSizeInMB
                'Size(GB)'    = $totalFolderSizeInGB
            }
            $folderList.Add($folderObject) | Out-Null
        }   
    }
    Return $folderList
}