Why "Ar ôl i mi godi"? Why can't you just say "Ar ôl dw i'n codi"?
It is just that the the pattern with i is the one which has come to be used in Welsh to convey that meaning. A similar pattern is used to convey many other meanings, too.
Welsh and English have very different structures in some respects.
Thank you! :-)
There is further explanation in the notes for this section.