That's great advice.You need to talk to your building dept and see how they rule on it.
My guess is they will call it a detached garage and require that it meet the same requirements that a stick built, kit built, or modular garage would have to meet.
https://duckduckgo.com/?q=storage+shed+with+garage+door&iax=images&ia=imagesLet's have a picture, so we don't need to guess about what we are talking about.
The floor won't rot if it's made from the correct materials. Pole barns have their wooden support columns buried in the ground. The key is the correct amount of CCA, as I stated above.Never thought about wood floor rotting out.