u need roach speed/ good creep spread

IMHO, to play Zerg is to mean you need to gain advantage during early game, advantage here could mean cripple your enemy, or you have much more resources and/or units that your opponent.

Zerg - strong in early game, moderate in mid game, and weak in late game.

Terran - weak in early game, strong in mid game, and moderate in late game

Protoss - weak in early game, moderate in mid game, strong in late game

So you see, if you don't gain advantage in early game ... you're pretty much screwed later, because Zerg units are just slightly cheaper than other race, overall the price is the same. To outnumber your opponent also actually mean you are out-resource of them.

In my opinion, Zerg have 2 units that conquer in the early game -> zergling and queen.

Queen not only a good early defense for Zerg, but her spell - spawn larvae is almost a must for all Zerg, with 1 hatchery and 1 queen, you basically doesn't need to build extra units producing building.

Zergling in terms of resources, is the best tier 1 units, in equal resources ... it can basically wipe out other races tier 1 units ... provided if it's in open spaces. Furthermore other races unable to produce as much tier 1 units of Zerg in short time, thanks to the Zerg's Queen's spell.

So whenever I play Zerg, I will try to be aggressive in early game, because I always think if I don't gain advantage in early game, most probably I will be a dead meat entering mid game onwards.

need go hatchery to spawn larva using queen