I don't know really but for buildings people normaly cut and paste from existing structures. Some can make it from scratch but I don't know what they use.
Want to know what program can n use to design and make Structures and there animation unpacking and all that stuff.
You do know that "making Structures and their animation unpacking and all that stuff." is actually equal "a lot of work", don't you? There is no automated buildup-creation...you will have to draw/copy-paste/model each frame on it's own...