There is currently no parameter on the New-VM cmdlet for custom attributes (like there is for the Description property), but you can "pipe" the output of the New-VM cmdlet to the Set-CustomField cmdlet.
Something like this for example
New-VM -Name "PC1" -Description "PC1" -Datastore (Get-Datastore <dsname>) -VMHost (Get-VMHost <esxname>) | Set-CustomField -Name "Kostenstelle" -Value <some-value>