From Liquipedia Warcraft Wiki
The Goblin Laboratory is a Neutral building where you can purchase Goblin units, like Goblin Zeppelins and Goblin Sappers. The Goblin Laboratory is also a valuable tool for scouting, as you can reveal areas of the map for a modest price here.
Spells & Abilities
|Balance Patch History|
|Patch Version||Balance Changes|
|1.15|| Zeppelins are now available at the start of the 2nd day, rather than at the first nightfall.|
To purchase from a neutral shop or Mercenary Camp, a valid unit or Hero must now be within 450 distance units, down from 600 distance units. Note that this change does not affect racial shops.