EMS create room mailbox with resource custom set

Question

Hello!

I'm looking to make my job creating resource mailboxes easier. 

Since all my meeting rooms will have the same settings, I've written a script to take care of them.

However, I can't seem to get the resource customs set for the room.

Here is my script:

cls
Import-Module ActiveDirectory

# Create an array of your meetingroom resources

$roomResource = @("Videokonferanse", "Laserutstyr", "Gjestekontor", "TV", "PC", "Projektor", "Flipover", "Wifi", "Whiteboard")

## Variables ##

$roomName = Read-Host "Enter room name"
$userPrincipal = $roomName + "@testlabb.ad"
$office = Read-Host "Office location(In full name, ex: Porsgrunn)"
$capacity = Read-Host "Enter room capacity"
$resources = Read-Host "Room resources:ex(Videokonferanse, Laserutstyr, Gjestekontor, TV, PC, Projektor, Flipover, Wifi, Whiteboard)"
$resourcesArray = $resources.Split(",")
$resourcesTrimmed = ForEach($verdi in $resourcesArray){$verdi.Trim()}

# Create funtion
Function createRoom
{
[cmdletBinding()] 
Param( 
[Parameter(Mandatory=$True)] 
[string]$roomName, 
[Parameter(Mandatory=$True)] 
[string]$office, 
[Parameter(Mandatory=$True)] 
[string]$capacity
	 )
	 # Settings for room mailbox
	New-Mailbox -Name $roomName -Alias $roomName -OrganizationalUnit 'testlabb.ad/Exchange/Rom' -UserPrincipalName $userPrincipal -SamAccountName $roomName -FirstName $roomName -Initials '' -LastName '' -Room
	Set-CalendarProcessing -Identity $roomName -AutomateProcessing AutoAccept -BookingWindowInDays 365 -AddOrganizerToSubject $false -DeleteSubject $false
	Set-Mailbox -Identity $roomName -ResourceCapacity $capacity
	
	$roomEquipment = ""
	ForEach($room in $roomResource)	
	{
		ForEach($arrayItem in $resourcesTrimmed)
		{	
		
			if($arrayItem -eq $room)
			{				
				If($roomEquipment)
				{
					$roomEquipment += ","
				}
				$roomEquipment += $room				
			}	
		}		
	}

	$roomEquipmentArray = $roomEquipment.Split(",")
	$ResourceMailbox = Get-Mailbox -Identity $roomName
	ForEach($equipment in $roomEquipmentArray)
	{		
		$ResourceMailbox.ResourceCustom.Add($equipment)
	}
	
	Set-Mailbox -ResourceCustom $ResourceMailbox.ResourceCustom.Add
	
	#Set Office location
	$user = Get-ADUser -Identity $roomName
	Set-ADUser -Identity $user.SamAccountName -Office $office
	
}

# Run Function
createRoom -roomName $roomName -office $office -capacity $capacity

The part I'm having issues with is this:

$ResourceMailbox = Get-Mailbox -Identity $roomName
	ForEach($equipment in $roomEquipmentArray)
	{		
		$ResourceMailbox.ResourceCustom.Add($equipment)
	}
	
	Set-Mailbox -ResourceCustom $ResourceMailbox.ResourceCustom.Add

I'm getting this error message:

Cannot process argument transformation on parameter 'ResourceCustom'. Cannot convert value "System.Void Add(string item
)" to type "Microsoft.Exchange.Data.MultiValuedProperty`1[System.String]". Error: "Conversion from System.Management.Au
tomation.PSObject to System.String has not been implemented."
    + CategoryInfo          : InvalidData: (:) [Set-Mailbox], ParameterBindin...mationException
    + FullyQualifiedErrorId : ParameterArgumentTransformationError,Set-Mailbox

Can anyone help me?