There are games that legit start with v1.0 then v2.0 etc, even in their Alpha, really no pattern to that. Would be nice at the very least if those numbers actually meant something (either having your game be sectioned into chapters of aproximate equal length or in equal parts that are reflected in the versioning of the releases, eg: having 10F in your Tower, and adding a 0.1 to the version for each floor made). Best way to do it imo, with no specific length in mind for your game (I'd say that in of itself is kind of an issue but so long as it works...), would be by simple incremental versioning (like v10,v11,v12 etc), up until you declare the final version as being "Final" (and also with few situations for using decimals, so that u don't end up with a v69.420.1337.80085).