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RoA or Rylai (I prefer the latter, but this one's up to you - CC or HP?)
Boots of choice, how many options are there anyway? Most likely merc treads.
An MR item of your choice - I favour Abyssal Scepter, but then my Fiddlesticks isn't especially tanky. Spirit Visage would go well too, since your tanking has to be very much based on EHP.
Situational last item based on opponent team composition - likely BV, possibly frozen heart against heavy AD, deathcap for extra awesome.
It's pretty much the same core as any fiddlesticks build, except deathcap goes to optional items.