The antonyms for the word "build-ups" can vary depending on the context. If referring to physical things, the antonyms could be "demolitions" or "tear-downs." In a more metaphorical sense, antonyms for "build-ups" could be "breakdowns" or "dissolutions."
Another antonym could be "deconstruction" which means to take something apart, dismantle or strip it of its components. Similarly, "reducing" or "shrinking" could also be antonyms, indicating a reduction or decrease in size or quantity. Overall, these antonyms suggest a sense of reduction or destruction instead of growth or accumulation.