SharePoint Site Collection Storage Size - Quota Usage Report using PowerShell

Requirement: Wanted to get a quick storage quota report on SharePoint sites on their allocation vs used space metrics to find out underutilized sites.

Solution: PowerShell script to get SharePoint site quota report!
If you want to get used storage space for a particular site collection, use:

Get-SPSite http://site-collection=url | select @{label="Size in MB";Expression={$_.usage.storage/1MB}}

To get storage data for all site collections, use:

Get-SPSite | Select Url, @{Label="Size";Expression={$_.usage.Storage/1MB}} | Sort-Object -Descending -Property "Size"

Get Site collection Storage assigned vs used for all site collections:

Add-PSSnapin Microsoft.SharePoint.PowerShell -ErrorAction SilentlyContinue

Get-SPSite | Select URL,`
      @{Name="Site Owner"; Expression={$_.Owner.Email}},`
      @{Name="Quota Assigned"; Expression={"{0:N2} MB" -f ($_.Quota.StorageMaximumLevel/1MB)} } ,`
      @{Name="Storage Used"; Expression={"{0:N2} MB" -f ($_.Usage.Storage/1MB)}},`
   @{Name="Percentage Used"; Expression={"{0:P2}" -f (   ($_.Usage.Storage/1MB) / ($_.Quota.StorageMaximumLevel/1MB ))}}`
   | Out-GridView -Title " Quota Report"

Report Output:
Note that the "Infinity" has occurred on sites with No quota assigned!

Add-PSSnapin Microsoft.SharePoint.PowerShell -ErrorAction SilentlyContinue

#Get all available Quota Templates
$QuotaTemplates = [Microsoft.SharePoint.Administration.SPWebService]::ContentService.QuotaTemplates 
$QuotaHash=@{} #Hash Array to Hold: Quota ID & Name
$QuotaTemplates | ForEach-Object { $QuotaHash.Add($_.QuotaID, $_.Name) } 

#Get All Site collections Quota
Get-SPWebApplication | Get-SPSite -Limit "All" |  ForEach-Object { Write-host $_.RootWeb.URL". Quota Assigned : "  $QuotaHash.Get_Item($_.Quota.QuotaID) }