>Where should these files be kept? In a plain folder where each revision gets its own subfolder named as the revision number?
Yes. Although revision number naming would be problematic if youre using git as it uses SHA1s to identify revisions, naming them with date.branch.author.sha1 might be better.
That means updating two separate locations with each build, using two different interfaces...
It just means having your VCS do the build and create the directory in a post-commit script.
Or you could just actually get a real CI system.