Alright, so I find Kha'zix to be an absolute blast to play. The build I've come up with has been successful 4 out of 4 times (I realize this isn't definitive proof of anything, but I've done well enough that I feel it's reasonable to share). While in each of these I jungled, I see no reason why it wouldn't work in top lane equally well (if not better).
9/21/0 running Smite + Exhaust in the jungle. Some combo of Flash/Ghost/Ignite/Exhaust in top lane (teleport is probably okay too).
Marks: Flat AD
Seals: Flat Armor
Glyphs: MR per Level
Quints: Movement Speed
The only difference between jungle vs top lane would likely be boots. As jungler I tend to go for Boots of Mobility. In top lane Ninja Tabi or Merc's will probably serve better.
Boots + 3 or 4 Health Potions to start
Buy Wards and Health Potions as needed
Tear of the Goddess
Glacial Shroud and/or Catalyst of the Protector
Upgrade Boots to BoM/NT/Merc's
Banshee's Veil (if you needed the MR and bought the Catalyst for it)
Final Build: Appropriate Boots, Manamune, Frozen Heart, Banshee's Veil, Trinity Force, Last Whisper.
Jungle Skill Order
1 - W 2 - Q 3 - W 4 - E
R > W > Q > E for priority after
Top Lane Skill Order
1 - E 2 - W 3 - Q
R > W or Q (depends on whether you want more sustain or better damage) > E
Typically I find myself evolving either W or E first. E for the insane jump increase and reset, or W for the AoE and ranged slow.
Generally, I evolve E at 6, W at 11, and Q at 16.
In Top lane, I'd evolve W or Q first, depending on which I was favoring in lane. Then evolve E at 11 and the other at 16.
Pretty standard: Wolves -> Blue -> Wraiths -> Wolves -> Red -> Wraiths -> Little Golems
Gank at any point during the path if you think it's a good idea. Remember to spam W as long as you have any health deficit in the jungle (but be sure to be close enough for the heal).
Ideally, you would jungle Kha'zix when your mid is a champion who doesn't use mana, so you can take blue buffs for yourself. Early on, Kha'zix is pretty mana hungry in the jungle due to the high cost on his W.
Alright, try it out if you're interested and let me know how it goes! (Remember, you can cast your other abilities while in the air from his E, which can catch people off-guard.)
*edit* link to build on leaguecraft: http://leaguecraft.com/lnk/1As