Roles of an XI developer ?

1) Develop the Technical Specification (sometimes part of Architect).
2) Develop the Interfaces according to the requirement
i. All ABAP/Java Developments.
ii. Design/Configuration.
3) Test the scenario.

What are the BPM tcodes?

Ans :SWF_XI_ADM_BPE,
SWF_XI_ADM_BPE_DISP,
SXMB_ADM_BPE,
SXMB_MONI_BPE.
what are the use of BPM patterns?
Ans: Patterns are more like example where u can refer to the IS or u can make use of those in ur scenario.
SWEQADM - Check Events.
RSWELOGD- Delete Event trace.
SWEL- Display Event trace.
SWELS - Switch on Event trace.
SWI1- Processes and work items.
SWF_XI_SXPR - Restart workflow with errors.
SWF_XI_SWI14 - To find workflow log by interface name &namespace.
SWF_SI_SWI2_DIAG -Diagnosis process with errors.