(When you skilled out all your skills)

Core
Helps you ganking because you will pass the runespots anyway. When you stay on your lane at the beginning you can check the runespots easily with your blink. Storing runes is always good.
For obvious reasons. Can be delayed for Null Talismans.
Get 1 or 2 Null Talismans for mana (you really need it) and a health. Some people now maybe ask : "Why not bracers?" Bracers are good on many intelligence heroes. And they are defenetively not bad on Akasha. But Null Talismans are better. You need mana for Blink. And Blink prevents you better from dying than Hp ever could. Also intelligence gives you damage that helps you lasthitting (your animation is good but your damage is low).
Optional
I don't added it to the core items, because you sometimes need it, sometimes you don't even have to buy it and sometimes you don't have a scroll in you inventory. But I highly recommend to carry always 1 or 2 with you. 135 gold can save you (blink away and use it), towers (blink to a tower, lol) and allies (Give them one or use it to kill heroes that chase you friends into towers).
I really learned to love it. It can help you ganking (ganked heros use their skills^^) more often and helps you against spamming heroes like Zeus or Bristleback.
In early game team fights (not good in lategame) you will get many charges. Look in the "How to use" part. You can swap a Null Talisman with this item or just add it.

Core
When you need more disable in your team (i personally think that you can't have enough), build Guinsoo's. It's THE item for nearly every intelligence hero in lategame and should be your first aim after core because it gives you the only important thing that Akasha doesn't have: A disable.
It gives you in combination with Blink superb mobility to gank and destroy creepwaves.
Optional
Instead rushing a Guinsoo's just with a Void Stone, you can build a Ring of Health to get this. Is a good choice if you really want to focus on ganking or want to make a Linken's or a Hood (i know, that is wasted gold but it worth it I think).
It is an often underestimated Item that is great on Akasha, especially when you play against heroes like Riki.
It gives you strength and intelligence and the 2 baby warlocks are a great help by ganking. Blink, summon , Shadow Strike, Scream of Pain and hit, hit , hit to death. Also you can kill annoying wards. Skip it if you have serious problems to micro, there are no invisible heroes or you don't need to kill wards. It also counters heroes heroes like Luna or Yunero a bit because they prevent you and your team a bit from damage and AoE heroes will think twice about using skills because they don't want to damage/kill themselves (Don't think that it really saves you from it. 600 damage (after reduction) aren't that scary).
Eul's is a possibility, too. Since 6.60 you can use it on allys. This way you can not just disable dangerous targets, you can also save allys and use it on yourself when you see that you blinked in to hasty and would die. The mana regeneration is something you really need and more ms can't be wrong.
Luxury
Shivas let you tank a bit more and gives a nice aura which is annoying in combination with Shadowstrike. A bit more Aoe can't be wrong, too.
Good synergy with Shadow Strike. Gives you also a bit hp, mana and ... ok you don't really need attack speed but agility gives you also a bit armor.
It's also possible, because it's cheaper in 6.6x and Sonic Wave's cooldown is ways too high. I'm still not a fan of this, but if you like it, why not? You can buy a really helpful Point Booster in early game after core items and build Guinsoo then. Also you can rush Guinsoo without Point Booster or rush Aghanimn's instead of Guinsoo's. Impossible is nothing^^. All in all you should know what you spend your money for: You can always use your Ultimate in clash-orientated games. The damage is not really imba, Shiva's one is higher. And the stats are fairly nice, Life and Mana are the 2 things you mainly need.

*Update 6.64: Power Treats gives you attack speed again, so you can buy it.

Core
It can be easily build up and the Oblivion Staffs are granting you improtant mana regeneration for ganking. Soul Burn has a good synergy with your skills (more damage on 1 target than with Aghanimns).
You want to make physical damage, so Power Treats are a good choice for this build.
or
As I said in the Supportive Build, it's awesome for Akasha.

Now you have good attackspeed. So lets incrase your damage with a Stygian Desolator.
Or
As I mentioned before the synergy with Akasha's skills is great. And a slow cant be better than pure damage. The stats make you not so squishi.
Or
Also a choice against heroes that have evasion or Butterfly. It has problems with Stygians and Skadi's orb effects. So just buy it if your play against evasion heroes. Buying Stygian instead is better than deactivating the bonus effect, i think.

Optional
Good synergy. Gives you in fact a little extra Blink, that you don't need, and the stats are perfect (damage, intelligence and attack speed), but low. You CAN'T push someone on cliffs. In fact it's nothing more a fun item.
Luxury
If the game isn't over you can buy a Assault Cuirass because of the good synergy with Stygian Desolator (is good with Skadi, too) the amor buff is useful, too.
It is indipendent from agility now. If you build Skadi, it's a good choice.
Pure damage. Simple but good. Buy this, if you bought Desolator, because the pure damage let you make higher red numbers than Skadi.

Against nukes like Laguna Blade. Upgrade it to if you have the money.
Always a good choice. Gives you nice stats, regeneration and prevents you from some stuns (be fast and use Blink to save you then) and sometimes from hard damage nukes like Laguna Blade.
Against mass disables / nukes. Is good for the semi-carry build, because you will be a main target of disables / nukes even more and the damage/hp is good for you, too.

8250 gold. 800 damage. Useless in lategame. Buy Guinsoo's and Travels instead. Or Power Treats and Stygian. And you COULD buy Divine Reaper and Hyperstone for that money.
You aren't a tank. You can get mana and mana regeneration with better items like Guinsoo's.
Year imba double ultimate ... not. Not enough mana.
/ You ARE item dependent. You NEED your coreitems or you can not gank enough (since Icefrog nerved her clash-power the good combination of nice ganking and fairly good Aoe damage is nearly the only good reason to pick her). Let other heroes like Maiden, Warlock or Demon Witch buy this.

Reduces your damage to a minimum. You will just make around 375 damage with your Scream and Wave on in a teamfight.
250 heal is not as annoying as Pipe is but it's bad for you, too. Let you make 675 damage with Scream/Wave. Pipe+Mekansm let you make incredible 125 damage .
You have nothing to interrupt this.
As i said before, disables counter you. Eul's is not that bad. You can refresh your cooldown while be cycloned. But a chainstun after that is also your dead.
All your advantage in ganking is useless when the whole world see you.
Another perfekt counter item. You can't nuke and Blink, and you get extra damage from nukes.
I started hating this thing. If you do your SoP+Ulti combo on 1 guy with Blademail, you are nearly dead. If you hit 2 guys with Blademail, you are dead. (And when you have an AoE based team, and you hit 5 guys with Blademail, your team is dead).