If you have an idea for a unit paper that you'd like to talk to me about, or if you've already written a draft that you want to revise into a unit paper, or if you are in a seminar I'm teaching and might want to do a unit of any sort associated with that seminar, the best thing to do is to stop by my office hour (listed on my web page) for a quick chat. Do this early in the semester. (No need to email in advance for this--just stop by during the office hour.)
During our chat, I can advise you on whether the idea makes sense as a unit paper, and on who would might be good advisors for it. If it makes sense for us to work together topic-wise, then most often you can just get started on thinking about and writing the paper after we talk. On rare occassions I may be working with many other graduate students on unit papers---if so, I apologize in advance if I have to ask to work with you on the unit during a future semester.
To get credit for a unit from me, it should be done by the end of the academic semester, which is the last day of exams. Indeed, this is the official deadline for unit work--- final drafts are due on the last day of the undergraduate examination period each semester.
My rough guide is that a unit represents an amount of work equal to a substantial term paper for a one-semester graduate seminar. If you are starting from scratch, a good way to work on the unit is to start on it early in the semester, and to give me a substantial draft by about the middle of the semester. That way, you will have time to revise it or write another draft in the light of my comments. The number of revisions necessary varies: sometimes just one round is enough, but sometimes many revisions are necessary. Since there's no way of knowing in advance how many revisions it will take to get the unit, get that first draft in early.
If you don't get some kind of draft in around the middle of the semester, you shouldn't count on getting credit for the unit for that semester (though it is possible that you will). Protect yourself by staying up to date on your units, and avoid the stress of having to scramble at the end of the semester to catch up.
If you don't get a unit done during one semester, we can resume working on it together once the next semester has started.
When you submit a revision of a paper I've already read, please send along a version with significant changes indicated. In other words, format in boldface (or another distinguishable way) those passages or regions with significant changes/additions.)