Here it goes:
I think that by saying "I will become whole" he meant that he'll have the full power of the SOT6P
1st step is gaining the sharingan(he's an Uchiha so its only natural for him to have one).
2nd step is to get his hands on the the body (he gainded it after fighting Harashima Senju somehow)NarutoBase.net - Naruto Manga Chapter 510 - Page 12
3rd step is to implant the rinnengan or fuse the rinnengan with the sharingan,I think that his eyes look like his current mask so its not quite the juubi's eyes yet(its an incomplete form of the juubi's eyes)NarutoBase.net - Naruto Manga Chapter 511 - Page 17
4th step is to get his hands on all the tailed beasts and fuse them so he can seal all of there chackra within his body in order to have everything the sage had(i think that will also make his new set of eyes complete)
(its says here that Madara takes one step closer to becoming complete so all thats left is to seal the beasts chakra within him)
Sharingan+body(the power of the SOT6P body)+Uncomplete juubi's eyes+the chackra of all the tailed beasts=becoming whole
P,S i created the thread very quickly so im sorry if there are any mistakes in what i said.