One way to gain experience is to apply for an internship.  Many companies here in the U.S. offer this opportunity to students.  It usually takes the form of working for a company for a short period of time under the guidance of an architect.  This period of time normally equates to one or two university semesters.  Internships can be paid or non-paid.

You say you would like to become an architectural CAD technician which is fine and noble.  However, in the very next sentence you say you plan on studying Inventor and parametric modelling.  While that's nice I can tell you that you won't find many architectural firms using Inventor. 

If you are a student many universities post available internships.  Are you currently a student?