If you really want to roll with level 0 characters, you can go this route.
Step One - let them pick a class
Step Two - Let them pick a backround
Step Three - Give them the standard array to put where they wish.
In play, give people a chance to read magic scrolls, use wands, use weapons, practice skills, etc. And at the end of the adventure, let them take 1st level in any class they want. I would try to make sure the adventure is mostly traps and challenges rather than combat, and the whole thing should be worth about 50-100xp each.