For the builder in buildcraft 2 - see this.
NOTE: Since BC 3.4.2 the builder has been disabled due to major bugs. (This is still the case in 3.7.1)
A builder is a machine that, when powered, will automatically build a structure based off a blueprint, using resources supplied by the player. As a note, the blueprint does include the types of blocks in the original template, different from the way this worked in buildcraft 2. Once placed, a stone pick or greater is required to retrieve the builder.
Produces: 1 x Builder
UsageEditPlace the builder in your world, and right click on it to display the builder interface. Place a Blueprint into the template slot.
Alternatively, a builder can also be used to automatically build many repetitions of a structure, e.g. a path segment, by placing down and activating pathmarks, then placing the builder adjacent to an activated mark.The area that the Blueprint uses will be displayed in the world so you can adjust the position of the builder if needed. Put some resources into the builder, and supply some power, and the builder will automatically build the structure from the template. A steam engine or greater can power a Builder. 2 green status combustion engines burning fuel are required to fully power the builder. At this power level, the builder will place approximately 350 blocks a minute, or 5 and a half full stacks. If there is something in the area already, the builder will either remove it if it is not part of the template, or leave it there if it is. Blocks removed this way will remain on the ground, they will not pop out of the builder.