W/Q's EMP is great against heroes with low mana pool. Unfortunately, Invoker's low damage base makes it very difficult to farm and level without exort. If you have 3+ carries on your team, go W/Q, but that game is probably too hard to salvage. This build has very good crowd control, but you are unlikely to get kills in a team clash.

You may use this build only if your last hits won't be dominated.

See my comprehensive guide here:
http://www.dotafire.com/dota-2/guide/grimorums-guide-for-invoker-5924