$xmlWriter = New-Object System.XMl.XmlTextWriter('c:\temp\sitemap.xml',$Null)
$xmlWriter.Formatting = 'Indented'
$xmlWriter.Indentation = 1
$XmlWriter.IndentChar = "`t"

$xmlWriter.WriteStartDocument()
$xmlWriter.WriteStartElement('urlset')
$XmlWriter.WriteAttributeString('xmlns', 'http://www.sitemaps.org/schemas/sitemap/0.9')

$everythingUnderHome = Get-Item master: -Query "/sitecore/content/Home//*"
$baseUrl = "https://example.com"

$everythingUnderHome | ForEach-Object {

    $url = $baseUrl + [Sitecore.Links.LinkManager]::GetItemUrl($_)

    $xmlWriter.WriteStartElement('url')
    $xmlWriter.WriteElementString('loc',$url)
    $xmlWriter.WriteEndElement()
}

$xmlWriter.WriteEndElement()
$xmlWriter.WriteEndDocument()
$xmlWriter.Flush()
$xmlWriter.Close()