The majority of the projects I do call for an attic truss over the garage, however there are those instances where what you describe is exactly what the homeowner wants.
I am unfamiliar with any requirement in the IRC that requires an opening to be rated. I might ask the question "Rated for what?
If you are referring to the attic area as a storage area being rated, then yes, if it is called out as an attic storage area (according to the IRC) the required rating of 20#LL and 10#DL is typically applied and an attic ladder listed for use in this manner is installed.
However, you should also be aware that many jurisdictions require all garages attached to homes have rated fire walls separating attic areas of garages from the attic area of homes as per NFPA-101 or a fire rated separation from the garage to the attic, in which case most attic accesses would be precluded from being used in garages.
You probably should consult the NFPA-101 and the IRC a little more in depth to determine if these instances apply to your specific circumstances.