The build order
*from TeamLiquid forums*
(Optional early drone scout)
15 Spawning Pool
(Optional 0-6 Zerglings)
(Optional Metabolic Boost research)
@150min Roach Warren
Overlord x2 (Optional x1 if you made 4-6 lings)
* If you opt for 6 lings, you can allow meta boost to finish, and not impact your roach timing.
* Be sure you have OLs spotting the ramp. Due to your map control, you should be able to position two overlords (one on either side of his ramp).
I like it because it's tricky - it shows the player one thing, and does another thing. Perfect scouting would cause this not to work, and it wouldn't work against Zerg, because without a Queen to chase away the Overlord, your opponent could simply park an Overlord above your base and see everything he needs to see.
I've also been having an issue with ZvT lately (stupid bio pushes!) so this might be a good, aggressive answer to Terran stim pushes.