This guide is for Build Buster
which requires you to kill a Hyperion Constructor robot before it manages to build any additional robots.
The constructors are large yellow robots with a big red eye in the center, a picture of it is the trophy image. You just need to find one, and kill it quickly. This may be harder at lower levels as the fight with it might take longer, but once you are several levels above it and have some decent powered weapons, you shouldn't have any issues decimating it quickly.
I found I was unable to destroy the Constructor during the mission you free Roland, but was able to get it later in the game when you fight Hyperion enemies in the Highlands.
You can get plenty of Constructor spawns later in the game if you go into the Hyperion circle of slaughter. It's located in Ore Chasm, which is within the Eridium Blight area.
I believe Constructors spawn in around rounds 3-5.