Wand Focus: Builder is a Wand Focus/Research available after researching Wand Focus: Equal Trade
To first use Wand Focus: Builder, you must first sneak and right click on a block that you have in your inventory. The block and the amount of it in your inventory will replace the wand focus display (in your top left corner when holding your wand). A line will appear signifying where blocks will be placed when you press right click, up to 16.
To craft Wand Focus: Builder, you will need an Arcane Workbench.