Nothing can travel at the speed of light. As of today, that is one of the foundations of physics. The fastest theoretical speed scientists think can be achieved for micro spacecraft with light sails is about 20% the speed of light (and I've heard nothing about them being able to slow down). Transporting actual materials to build with is unlikely be a use of the astronomical energy required to move something large that fast, and the high opportunity for space debris to destroy it, again, because of the speed.