Sylvie,
So these costs would ultimately within ATUM 2.0 would roll up to Compute - Servers. However, I would recommend since these servers are much more expensive than a standard servers that you would add a metafield (i.e. Resource Metadata Field 1 in the Resource Towers) to add an additional level of granularity to call out these specific servers. So it would be something like this for your Tower \ Sub-Tower \ Metadata (Compute - Servers - Palantir)
At the servers level you could create your relationship that would include the metadata that you created in the IT Resource Towers so you on spread the Palantir costs over the Palantir servers.
This way you can still keep the granularity as you would spread these costs up the model and not blend all of your other severs together (such as windows \ linux).
Cheers,
Ryan