How in the heck do they do that?!

How in the heck do they do that?!

I have have a problem with unit stocks in taverns/altars. I am more or less trying to do the same sort of hero/unit selection that you see in alot of current maps including DOTA. A unit is chosen from specified building and once chosen is removed from the building so that you may not have duplicates of the same unit. Picked unit is then created at a starting location for the player that clicked the icon in the building. Any help anyone can give me is much appreciated. Thank you.

Two ways:

1 - Remove the unit from the tavern's stock (one of the actions under Neutral Building or something to that effect does it)
2 - The way DOTA does it: After a unit is selected, restrict the training of all players for that unit to 0.

Classify the tavern as a marketplace. Marketplaces can be tweaked with triggers to add/remove units and/or items

Don't even need to do that. Just give it the Sell Items or Sell Units ability. All of the heros in my upcoming map "sell" wisps.

Thanks alot for your help =)