Outpost Building Assembly Notes

Outpost Building Assembly Notes is the currency for purchasing level 2 Garrison Blueprints for small and medium buildings. Up to two may be acquired via quests in Gorgrond and Spires of Arak. Blueprints for the fixed common structures (the mine, the fishing shack, and the herb garden) are not available this way and must be purchased for at the garrison's town Hall.

Source
This item is a quest reward from the following quests:
 * No Time to Waste (quest)
 * Strike While the Iron is Hot
 * The Ebon Hunter (quest)