^ in dom its pros ring XD lol.

Rushing Deathcap on Diana is perfectly feasible due to her shield.

pros ring > ionian > kage pick > DFG or deathcap > DFG or deathcap > lichbane

turn on shield before you R in to survive the initial CC/burst

For starts, do NOT build RoA on her. Sorry but as much as the item is good on AP, you're better off rushing Deathcap rather than rushing this.

My build always begins with Prospector's Ring, Boots, and 2 Red Sodas ()

Build her boots according to the enemy team's composition: If you see a ton of AD and a Xin, go with Tabi boots. A lot of CC or AP? Go Merc Treads.

From here, you can build according to what you like. I generally rush Cap because it syncs perfectly with her shield and gives a bigger boost than anything. A lot of people state that Void Staff puts out more damage so get this over Deathcap, but I'm highly inclined to state that while it does provide +40% Magic Penetration, it provides 110 (at the very minimum) less AP than the Deathcap, which means you have a weaker shield, weaker passive, and weaker abilities at general, and you'll still be squishy regardless to if you rushed Void Staff over Deathcap once that shield dropped or you get CC'd. Build a void staff ONLY when the enemy begins to build MRes (preferably after you build a Deathcap).

From here, you can do your spec how you want. I prefer to nuke, so I get Deathfire Grasp (since with Deathcap you can do an easy 40% of their health in damage before you even land your Q>R>W Combo), followed by Lich Bane, then depending on the enemy team comp another CDR or Defensive item (usually FH or Athene's fits well).

My build goes:
Prospector's Ring
Merc Treads (or Ninja Tabi boots, or even Sorc shoes if you can play aggressively without any needed defense)
Rabadon's Deathcap
Deathfire Grasp**
Lich Bane**
Frozen Heart, Void Staff, or Athene's Unholy Grail**

** = Items can be interchanged in terms of building order based on if more defense is needed than offense, and if more Armor or MPen is needed.

This is just my nuke build, usually even without Void Staff I can usually burst down someone with one combo. I usually don't ever feel the need to build a Rylai's because so long as I'm able to ult to them they're usually dead or running away (at which that's what her E is for), but I definitely would say build it if you need it (it's all personal preference).

Then again, I usually only play bot. Some use Nashor's Tooth up top, I personally think it sucks in terms of damage output (In comparison to getting it over Deathfire Grasp, you're trading out -15 AP + another nuke that synergizes perfectly with her initiating combo for 10% more CDR, +10 mana regen, and 50% AS that at level 18 effectively reduces the number of hits needed for her passive to hit from 3 to about 2.7 which isn't big at ALL)

Rushing deathcap is never viable if you want to have a good early game. I regularly wreck with Diana. She should be built as an AS/AP hybrid, because her passive scales ridiculously well.

Beserkers greaves+ tome+ two health pots

Fiendish codex + Malady

Nashors+ Rylais

Lichbane if there is time

This build is squishy as hell, no way are you wrecking anything unless people are just not targeting you whatsoever. Not to mention Magic Resist cancels out your build heavily, and unless you're at the ELO where people don't build Frozen Heart, all it takes is simple CC and you'll squish (without doing much damage) faster than Teemo.

Ive played her 5 games 3 of which bot and i have yet to manage to get even close to running out of mana.. use the packs and your fine.

there's a dominion build in here somewhere

Thanks for all the replies. I hope to try her again this weekend. It does appear that there is still a good deal of controversy over her build though. :-)