VMShutdown.ps1

# Author: Garth Jones
# http://www.enhansoft.com
#
# Created Date: 2016-08-01
# Version: 1.00
#
# Thanks Sean Kearney @energizedtech for the start point. 
# 

##################################################################
#                   User Defined Variables
##################################################################

Clear-Host
$CSVPath='C:\temp\'
$CSVName ='computerlist.csv'
$Downtime = 5
$Uptime = 60


# Test for the CSV file
if (test-path -Path $CSVPath$CSVName)
{
    $Start=$True
    write-host "Starting VM"
}
else
{
    $Start=$False
    write-host "Stopping VM"
}

# Starting the VMs
If ($Start)
{
    $vmlist = Import-CSV -Path $CSVPath$CSVName

    Foreach ($VM in $VMlist)
    {
        write-host "Starting VM: $VM.VMname"
        Start-VM -Name $VM.VMname 
        write-host "Sleeping $Uptime seconds"
        start-sleep $Uptime 
    }
    Remove-Item $CSVPath$CSVName
    write-host "Deleting: $CSVPath$CSVName"
}
else
{
# Staopping the VMs
    New-Item -Path $CSVPath -Name $CSVName -ItemType File -Force
    Add-Content -path $CSVPath$CSVName -value VMname
    GET-VM | where {$_.state -eq ‘running’} | Select-Object -expandproperty Name | foreach { Add-Content -Path $CSVPath$CSVName -value $_} 
    $vmlist = Import-CSV -Path $CSVPath$CSVName

    Foreach ($VM in $VMlist)
    {
        write-host "Stopping VM: $VM.VMname"
        Stop-VM -Name $VM.VMname -force
        write-host "Sleeping $Downtime seconds"
        start-sleep $Downtime

    }

    write-host "Rebooting Server"
    
    # Reboot the Server 
    # Uncomment the next line to reboot the server

    # Restart-Computer -Force
}

Having a Priority property on the VM would help. This should be a unique value.A VM with a Priority of 1 would start 1st and shut down last. A VM with a priority on 1000 would shut down 1st and start up last.
You could mock this feature up with a config file to hold the priority until the feature is added to Hyper-V. The script could read the config file and look up the vm and add the priority to the computername.csv that would allow you to sort on the priority for the startup and shutdown actions,