this is the PowerShell script that deletes every resource in a given resource group. It was demonstrated in my video about Azure Automation in the Azure Advent Calendar series (https://www.youtube.com/watch?v=N1ktTy08xDs)

Empty-Resource-Group.ps1

workflow Empty-Resource-Group
{
    param(
        [Parameter(Mandatory=$true)][ValidateNotNullOrEmpty()] 
        [string]
        $ResourceGroupName,
        [Parameter(Mandatory=$true)][ValidateNotNullOrEmpty()] 
        [String] 
        $SubscriptionId 
 	)

    # Login to Azure    
    $connection = Get-AutomationConnection -Name AzureRunAsConnection
    Login-AzAccount -ServicePrincipal -Tenant $connection.TenantID `
        -ApplicationId $connection.ApplicationID `
        -CertificateThumbprint $connection.CertificateThumbprint 
    
    Select-AzSubscription -SubscriptionId $SubscriptionId
    Write-Output "Connected to Azure!"

    
    #Get the Azure Resource Group
    $rg = Get-AzResourceGroup -Name $ResourceGroupName;
   
    if(!$rg){
		Write-Output "Resource Group $ResourceGroupName does not exist.";
	}
	else{
        Write-Output "Deleting resources..."
        
        # Get all resources in the resource group
        $resources = (Get-AzResource | where { $_.ResourceGroupName -match $ResourceGroupName });

        Foreach -parallel ($resource in $resources) {            
            if($resource.ResourceType -eq 'Microsoft.KeyVault/vaults' -Or $resource.ResourceType -eq 'Microsoft.Automation/automationAccounts' -Or $resource.ResourceType -eq 'Microsoft.Automation/automationAccounts/runbooks') {
              Write-Output "$($resource.Name) - won't be deleted"
              # instruction 'break' is not supported in Azure PowerShell Automation
            }
            else {
                Write-Output "Deleting - $($resource.Name)"
                Remove-AzResource -ResourceId $resource.ResourceId -Force
            }
        }
    }
}