trigger help

Ok, i need some trigger help here i am making it so every 20 seconds 18 units are created, (thats part is fine) however when you build a certain structure, those units get upgraded and now come every 25 seconds, so its a stronger unit, but is generated every 25 seconds. and finally you can buuld a 3rd building enabling even stronger units every 30 seconds. But i cant figure out how to stop production of the lvl 1 units and move onto lvl 2 and this is the same for diabling lvl 2 and moving onto lvl 3 and im nto sure if the even would be a Time -periodical event or some other thing that has to do with a buulding being built. So if anyone could reply to this and post what they think should be the correct Events, Conditions, and Triggers; i would be eternally greatfull =)

Let's start:

Event: Every 20 seconds
Condition: Level1Units = True
Action: Create 18 Sheep in region Farm.

Now, just say someone built the building.

Action: Set Level1Units = False
Set Level2Units = True

The level 2 units:

Event: Every 25 seconds
Condition: Level2Units = True
Action: Create 18 Steel Sheep in region Farm...

It keeps going until you want to stop it :)

I forgot 1 more thing, how do i get rid of workers at the beginning? and make it so when i set my start locations the town halls dont actually show up...????

Simply no Town Hall on the start location? Delete all the melee triggers and make sure the map ISN'T a melee map (bottem right corner shows it)

ALL the melee triggers? cuz i still need to set starting resources and run melee AI script for comp, also any suggestions on my other trigger stumper?

Ok, nm for the lvl 2 i figured out a way, but it wont work for lvl 3 so i still need some help there

Same thing over again. Make sure you turn off the 2nd production thing boolean.