Build item basics
A build item improve the performance or capability of a building that it is assigned to. Every building has its own special build item. Usually you may reach a level 10 in build items, but you will have to do research first. Most build items can be upgraded to up level 10. Effects are not cumulative, only the effect of the highest level matters.
The construction yard
Build items cannot be won in events, they must be crafted in the building called "construction yard" (you will be able to build a "construction yard" when you reach level 45) this will let you craft build items. You will have to build a "construction yard" in every kingdom that that you want to craft build items for its buildings (but not in "Storm Islands" or "Berimond").
The materials that are needed to produce and create build items can be obtained in various ways: As rewards from events that you participate in, buying them directly from the "Master Blacksmith" (using your gold & silver pieces), by trading special event currencies of "Samurai" and "Nomads" events or from the "Armorer" directly (using rubies).
Crafting regular build items
There are 6 materials that participate in the crafting process for regular build items:
Every craft of a new build item, requires that you have the previous level item. Every level will cost you more materials . Once a build item is crafted you may assign it to the corresponding building without any additional costs, however removing a build item from a building costs you gold coins. You may also destroy a build item that you do not need, and get back half of the resources.
Crafting Relic build items
There are 12 additional materials that participate in the crafting process of relic build items:
The keep — "Wall capacity build item" will give you more troops on the wall when you defend an attack. This is very important in the game. The maximum level of this item is 10 and will allow you to have +55 troops on the wall. I recommend that you have a this build item in every castle or outpost to maximize your defense capabilities. You may buy a level 12 of this build item in "The armorer (+75 troops on wall) for 79k rubies.
Bakery — "Food storage build item" will give you more food capacity in your castle. This will allow you to have more food hence have more troops. The maximum level of this item is 5 and will give you more 12,000 food capacity (total of 93k). However, you may win a higher level of this build item in events. For example a level 7 will give you +20k food (total of 101k)
Granary — "Food production build item" will give you more food pre hour. This will allow to to produce more food hence have more troops. The maximum level of this item is 10 and will let you produce +200 food per hour in your granary (or farmhouse).
Note for advanced players: There is another build item, which you can only win as a prize in events (but you can not craft) which increase the "Base food production" bonus. In a very advanced stages of the game, where your granaries will be at very high level (25-30) you will find that using this build item (levels 7-9) will function much better than the one you can craft on granaries with 43-100% production.
Barracks — you have 2 options: "Recruitment costs build item" which will allow you to recruit at cheaper price (-40% cheaper at level 10) or "Troops per recruitment slot" which will allow you to recruit more troops (maximum level 4 with +80 troops per slot).
Marketplace — "Market barrows build item" will give you more "market barrows" hence the ability to move more resources between your castles/outposts. The maximum level of this item is 10 and will give you +40 more barrows).
Drill ground — "Recruitment speed build item" will let you recruit troops faster. The maximum level of this item is 10 and will let you recruit +110% faster.