Ready-made building (6)
I believe the answer is:
prefab
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">ready-made building</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for prefab that I've seen before include "It's readily put together" , "Building easy to assemble" , "Building made for easy assembly (colloq.)" , "Factory-made building" , "Building assembled from manufactured parts, in short" .)