First build drones until you have 9 then build an overlord. You should have about 300 minerals when the overlord is done. Find an expandsion with a drone and build a hatchery. As soon as you get enough money build a spawning pool make 2 creep colonys later sunkens and keep building drones. When the expansions are finished, get 3 vespene gysers in your base and where your expansion is.Make 3 drones mine in each vespene gyser.While you get the vespene gysers up, build more sunken defence to hold the enemy off.When all the vespene gysers are finished(every single one doesn't have to have the drones mining them at the exact time)upgrade the hatcheries to lairs.You should have some money left so build a hydralisk den.You will have alot of gas so concentrate on getting more drones and build 3 more hatcheries in your main base.Once you get some nice cash flowing in,upgrade your overlords from all your lairs and get 2 spires.Build some more sunken defence and line the area of your main/expansion base with spore colonies(with the exception that you have alrready built evoulution chambers.),if you feel the need.If your oppenet has attacked you by now,build some hydras and maybe some 'lings for extra protection.If it's a BGH or Best Map Ever map,you could also build defence at the entrance(it would be better if you started a defence at the entrance early).Get lurkers then build a queen's nest.Once the queen's nest is done,upgrade all of your expansions to a hive.(To not waste money,the ones that are hatcheries just upgrade to a lair).Upgrade with one of your spires the attack or armor of air troops.While the hatcheries/lairs are upgrading,build 50 mutalisks,if it's not a real money map,get atleast 20-30.When the hives are finished,upgrade one of the spires to a super spire.If your money is getting low,keep making drones with the money left over from the mutalisks while they're hatching,do it until your money is constately coming in.If the mutalisks are taking too long for 50 try for 40 and under.Once your greater spire is done,immeaditly start upgrading.Then transform 30 of the mutalisks and 20 devourers(12 works great too).By the time you have that you should have a nice collection of overlords(if they are zerg you might not need them,but they can distract the enemy sometimes).When you at least have the guardians ready,scout for the enemy(if you haven't already found him)find all his weak points(usually the sides)and go for his main base.If you see he has to much anti-air build the other 20-10 mutalisks and make them devourers.By this time you should have upgraded to atleast level 2,if it's level three then good.It's time to attack(if you haven't already with hydras/lings or other..)If your getting to impatient(?)just go with the devourers you already have.Go to an island or place nearest to him and attack from the side,or if it's strong there,attack his front.Once you get rid of most anti-air go for his hatchery.For a bigger effect,send all your protection troops(or not if he's too big for the "little" army you have)(?).If you've attacked him from the inside out,destroy all the buildings left,or if he is too strong go back to your main base,find all his expansions and have fun :)

CreepColony's Opinion: If your opponent is going mass BattleCruisers or Carriers, build at least 36 devourers.