Maybe marada wanted to make a point:
Look everybody you call yourself Kages?... Sasukes MS is quite a bit weaker than mine... look at how much trouble he gave you ... in other words:
DON'T MESS WITH ME!
^^
We can probably assume that Madara want's more power ... of course he can't get power the easy way ... just like Orochimaru he needs some foolproof masterplan instead of going on and just taking the power ...
(I am pointing at my previous stupid Orochimaru rant... ^^ )
Got eat a Hyuga get the Byakugan
use the byakugan to temporarily disable kakashi
Eat kakashi
Therefore gain the ability to switch between Byakugan and sharingan
use this advantage to eat sasuke
^^
That would be about it... game over for konoha + akatsuki
Of course Orochimaru could also win by just using Suckimaru against Konoha ... Just.. chain him to Hokages home yattering about a place to return to and before long all of konoha would flee
