I have a 20'x20' or thereabouts. Plus mine has a sloping flat roof with NO "up in the rafter" storage. As soon as I've got some spare money (LOL) I'm gonna tear that thing down and build a decent size garage. What ever you can do to go bigger, DO IT NOW!!
With kids stuff, tools, lawn equipment, snow thrower, etc, I have NO room for anything.
Just my two cents worth.
John in Rochester NY.