For metal buildings (such as those from Irregular Miniatures) milliput can be used, although I haven’t had much to correct on them, as they are usually molded in one piece.
I confess that I am interested in MDF as a material for kits because of my toy trains. There is a type of brake van that I particularly want. It is available as an etched brass kit, and also (from another firm) a laser-cut MDF kit without a chassis. I don’t think that I am up to soldering etched brass yet. I think that I know of a resin kit that could be the basis of the chassis.