well,i dunno if it helps,but what i do is make drones till i hit my supply limit then i build 3 overlords and start building a spawning pool by my hatchery, then start making zerglings to defend myself. during the course of defending and attacking,i end up making at least 15 or 16 hatcheries and/or lairs. i usually make alot of mutas or hydras. or just random units
*hint* for fast kills and destruction or good D make 6 to 10 Ultralisks with upgraded armor.
works for me