Making Units Spawn - Upgrade

[Chris]

I played a map called Footmen vs Grunts. The war mills and graveyards on the orc teams have upgrades like Call Ghoul (when researched, creates one ghoul at the fortress every 50 seconds). I was wondering how that is done by either skills or triggers, all I know is that there is a condition that says if the upgrade was researched. (I am not very good with triggers yet, I am only really good with editing unit skills and constants )

[Darimus]

I'd make it a unit or spell that you can learn/create

After it's learned, wait 60 seconds (or a 60-second repeating timer), create 1 unit, repeat...

or it could be a perodic event trigger for 60 seconds