The word "prefabricates" refers to the process of constructing or manufacturing something in advance, usually in a factory or workshop setting. Antonyms for this word might include terms like "customizes," "tailors," or "personalizes," which suggest the opposite approach of creating something specifically for a particular purpose or customer. Other antonyms might include words like "improvises," "adapts," or "invents," which suggest a more creative or flexible approach to construction and design. Ultimately, the choice of antonym will depend on the particular context in which the word "prefabricates" is being used and the type of construction or manufacturing being described.