The word "un-build" typically implies an action of dismantling or tearing down structures, buildings or other constructions. Some possible antonyms of un-build include build, construct, erect, create, establish, form, or raise. When you build something, you are using materials and labor to put together a structure or object that didn't previously exist. Building and un-building are often two sides of the same process, as structures might need to be taken apart before they can be rebuilt or renovated. Therefore, antonyms such as build or create suggest a positive action that involves making something new or improving it, while un-build or destroy imply a negative action that involves undoing or ruining something that was previously built.