Item that gives new buildable unit or structure?

[Foxace]

How to make item that unlocks or creates new unit or structure that can be built from production facility like siege workshop?

 

[Maker]

Unit acquires an item
Item type == your item type
Player - Make Footman Available for training/construction by Triggering player

Unit loses an item
Item type == your item type
Player - Make Footman Unavailable for training/construction by Triggering player

Initially disable the construction availability for all players. The unavailability trigger might need to be more complicated depending on if the player has more than one hero and if there are more than one of the items.

 

[Adiktuz]

or make those buildings/units require a certain upgrade... then make a trigger such that when you pick/use the item, it then sets the upgrade for the player