One or more input/output devices accept user-inputted path instructions that specify a set of multiple deposition paths for an extruder to travel. An actuator actuates motion of the extruder along a trajectory that includes each of the deposition paths and also includes multiple non-deposition paths. For each deposition path: (a) the user-inputted path instructions specify a thickness of an object; and (b) the extruder extrudes the object in accordance with fabrication instructions computed by a computer based at least in part on the thickness. As the extruder moves over the entire trajectory, the extruder extrudes a set of objects, one object per deposition path. The objects adhere to each other to form an integral 3D structure. In some cases, the objects include functionally graded material.