The word "prefabbed" refers to something that is manufactured in advance or pre-made. When we talk about antonyms for this term, we can think of words that relate to things that are handmade, customized or created on-site. Some of the antonyms for prefabbed could be bespoke, tailor-made, crafted, or handmade. These terms refer to things that are personalized, unique, and made with individual attention and care. Unlike prefabbed items that are produced in large numbers, bespoke and handmade products are often one-of-a-kind and can have special significance for their owners. By choosing bespoke or handmade items, people can enjoy a sense of exclusivity and quality that is often lacking in mass-produced products.