Create Potential Supplier Create custom SFG

Hello, Experts!

I'm want to create SFG for DropDown ListBox. In the standard, this option is not avaible. I want to create this SFG in SRMSMC_SUP_EXTAR4 area. I create copy of standard class /SRMSMC/CL_EXTN_WD_SUP_INP. For creation dropdown list box component I want to use class CL_WD_DROP_DOWN_LIST_BOX. Unfortunately I do not know what parameters to pass on.

Thanks for any help.