As of right now, I have 224.5 hours in ours.
Build log here (with running total and description of time spent). . .
http://webpages.charter.net/outtahand/littletow/index.htm
The time should be FAIRLY accurate. I didn't use a time clock, but I tried to write it down every other day or so.
The trailer is basically done. I have a bunch of little things to do to it. I can easily spend another 20 hours on it. But it is very usable at this point. In fact, we've camped in it three times now.
So somewhere around 200 to 250 hours is probably a fair number, depending upon the level of intricacy and detail you plan. Another factor, naturally, is your speed of work. Some people work at things at a very leisurely pace with lots of breaks. Others go at it and don't stop for anything. Over the course of a trailer build, that difference could easily be 10 hours or more.
Another factor is whether you're going to work on it in 1 - 2 hour increments, or 8 - 10 hour increments. If you just spend a couple hours a night on it, you can easily spend 15 minutes per night just gathering tools and figuring out where you left off. That can add up to lots of extra hours overall. If you put in 8 - 10 hour days on it, you have a lot less of that wasted time.