Recently, I had a decent game (on SR) as the hat man 
with this build: 
, 
, 
, 
, 
, and 
. It was only until after the game that I noticed that I did not have 
but I could still two-shot everyone on the enemy team when 's active was up.
Are there any situations where you shouldn't/wouldn't buy ? What would you have dropped in the above build to make room for ?
The match stats are included.
no, rabadsons is actually very often outpicked by many other items by a lot of champions. for example, for swain, I will under no circumstances get a in my build. it can also be outpicked by magic pen items like 
etc, since they all (but ) give some decent magic pen, ap, and defensive stats like health or mr. rabadons is never something that you always want, its just a good item if you want a buttload of bonus ap, like 
soulstealer. I would very seldom "always" get an item, just leave it mostly for situational and for what your team needs most from you.
hope that helped :D
You wouldn't really need the D cap unless if your fed hard early game because items like what firedancer2000 suggested are usually bought because they are cheap and have decent stats to work with your champion.
i woulda drop void staff unless they have quite a bit of mr
Rabadon's is quite simply raw Ability Power. Nothing more, nothing less. Keeping this in mind, the only time you should build this is when you don't need any other stats/perks other than raw damage and/or won't for awhile.
As for the above build, Void Staff and Magic pen boots are what shredded through the small amount of mr that the enemy team did have, bringing you pretty close to true damage. Lich Bane is core. I don't know that both Zhonya's and GA were necessary, but if that was the case then more power to ya'. If you didn't actually need them both, then I would've dropped one or DFG(late-game). I'll explain why.
While DFG pretty much guarantees you a kill on one specific target (which is really important in lane and for roaming), Rabadon's 120% AP bonus synergizes really well with the Lich Bane passive and gives you a higher damage output to multiple targets throughout a team fight.
This is, of course, just my preference. Either way, your build accomplished the job that it was supposed to, which makes it A-okay,
