It's my experience that pad construction, like scribe, is
very foundry- (even flow-) idiosyncratic. Add to this the
differences between wirebond and bump attach and you
have enough variety that you need to go to the destination
fab, not the Distributed Fount o' Internetz Wisdom, for your
answer.
And of course gpdk has no foundry connection, right?
You could add your pad (silox, whatever) to the display
layer table and stream layer table, and fake it I suppose.
Still many low level style differences, like whether the
pad includes all metals or only top, whether the vias
between layers are standard or pad-cut-scale and
how dense, if standard, the nesting of metal layers and
any under-pad wells & guardrings, on and on.