Doubt about one Spell of TMRE and Creo Rituals

Hi everyone, on page 52 of TMRE talks about one spell, Craft Mechanism, that is group but actually you create one same object, others examples of Creo Form objects ( since theMystic Tower to the Basilic from A&A) the size and comlexity are the parametters to one simple object.
On the same sense, to enchant one castle and no the content, Structure or a very very big Individual?