[AxS.Sorathez]

in bronze i would suggest not worrying too much about what they are doing and just focus on your own macro.

if you macro well you could probably get to plat or diamond with just zealot stalker sentry.

This. This is mainly because it's not uncommon in Bronze for players to build things and never use them.
They might, for example, go gas first but do a normal (but delayed) MMM push (as Terran, whereas this would normally indicate a banshee rush), or as zerg, go gas first, get speed and then go mass lings for a while, without taking drones off gas (which would indicate a baneling all-in) and so on.
As such it's not necessarily possible to discover what someone in Bronze is doing because of this.

As such, just pick a build (one for each matchup) learn it, and practise your macro