Hi Alex,
You can find table size of any objects in BW on hana from DB02 transaction > tables and views, enter the table name to get it's size on disk and in memory.
You can also schedule a job from ST14 transaction to get the list of all largest DSO's, PSA and changelog tables.
Also kindly refer the following links which would be useful for you:
http://www.saphana.com/docs/DOC-2770
BW on HANA : How can i see the BW tables on HANA database
Hope this helps your query :-) Let me know :-)
with Regards,
Antony Jerald.