Ok, this may sound a bit strange, but you can also go for a fuckingspeedcritvoker. Kinda casting, ranged motred. It's quite easy: skill quas on lv1 and let it lv1, then max up invoke, wex (first) and exort (second), get buriza and invoke alacrity and you'll have over 1000 crit at lv25 with this buff. Due to the low cooldown and manacost, you can run around on alacrity half of the time, dealing hard crits with a damn epic attack speed.
AND you got your spells, means your a critDps-caster-hybrid. Same rules as for Motred, try not getting targetet and stay in back. Let your teammates tank for you, whilst you crit down all enemys in 5 seconds and those who run away will be finished by chaos meteor.
My invoker crit build looks like this:
2. Invoke -> cold snap (nice early gank spell)
7. Invoke -> EMP/ Meteor/ Sunstrike
17. Invoke -> Alacrity + Meteor
Heal yourself a bit up with 3x quas if necessary, for fights use 3x wex.
When you got buriza + mjollnir, go for 3x exort in late game.
Why exort? By skilling this up, you boost your int -> more dmg and mana.
You can try to find out the best exort-wex combo for critting.
Never got an ultrakill so fast, over 1000 crit output with 3x Exort.
Less crit dmg, but faster crits over time with 3x Wex.
This actually makes Invoker to a flexible critter, which is kinda unique.