Garuav nailed it - you want to use a policy definition.
https://azure.microsoft.com/en-us/documentation/articles/resource-manager-policy/
You will have something like this:
$policyJSON = @'
{
"if" : {
"not" : {
"field" : "vmSize",
"in" : ["Standard_D1", "Standard_D2"]
}
},
"then" : {
"effect" : "deny"
}
}
'@
$policy = New-AzureRmPolicyDefinition -Name 'VMSizeRestriction' -DisplayName 'VM Size Restrictions' -Policy $policyJSON
New-AzureRmPolicyAssignment -Name 'VMSizeRestriction-SubscriptionA' -PolicyDefinition $policy -Scope '/subscriptions/
(, resourceGroups) RBAC ( RG, RG). doc .