You could check (SWO1) business object WBS / BUS2054, it already carries the event "WBS created". To add the changed event you could create a ZBUS2054 as a subtype of BUS2054, and trigger the event (e.g. calling SAP_WAPI_CREATE_EVENT) in some WBS related BAdI or thru SBVW.
Of course you could also trigger your program in some BAdI.
Use search tool, I think there are already threads on this subject.
Regards,
Raymond