what exact steps did you do for Monitor details, and specific folder size, via inventory? Where is that info stored, when you look interactively on a client? wmi, or regkeys?
There are three paths, really, for adding to inventory.
Path 1:
if everything you want is already in WMI. This is the easiest; you just browse in default client settings, inventory, and add that class. (if you are using WMIMonitorID, a wmi class that already exists, then that might work for that; but you don't say what you are using)
Path 2:
If what you want are registry keys. Then you need to modify configuration.mof, and either import, or browse wmi (after configuration.mof is processed by that client).
Path 3:
If what you want is "the results of a custom script, where that script dumped the results into a custom WMI class or custom registry keys"; then it's multiple things, depending upon what that script did. The first step is to ensure that custom script ran at all on a client. Did it run, and populate wmi or regkeys? If the values are there now on a client, did you modify configuration.mof (if it was regkeys)?