In this article , Enable save as template page
#Get site url 

$web = Get-SPWeb http://peakfinders/
$web.AllProperties["SaveSiteAsTemplateEnabled"] = "true"
$web.Update() 
 Now you can able  access the save site as template :

/ _layouts/savetmpl.aspx

$web = Get-SPWeb "http://spserver/sites/Raghu/"
$web.AllProperties["SaveSiteAsTemplateEnabled"] = "true"
$web.Update()

when we document library [void][System.Reflection.Assembly]::LoadWithPartialName("Microsoft.SharePoint")
[void][System.Reflection.Assembly]::LoadWithPartialName("Microsoft.SharePoint.Administration")
$docSize = 5000000000
$webservice = [Microsoft.SharePoint.Administration.SPWebService]::ContentService
$webservice.MaxTemplateDocumentSize = $docSize
$webservice.Update()