Because I am in the class, we were given a special tour by one of the curators. We were able to go into the basement, spend a little bit longer in 'the new room', and also go up to the third floor! The third floor is rarely seen because logistically you just can't get a lot of people up there, and it would really block the flow of traffic for a sight that gets millions of visitors a year. The third floor is pretty special though. It's where Martha Washington moved her bedroom to after the death of George, and also allows access to the coupola. The curator at Mount Vernon said there isn't anything that indicated that a ladder was stationed at the coupola like there is now, but it definetly provided light and air flow for the house. Regardless I got to go up into it and I took a few pictures of the grounds from that great vantage point! I appoligize in advance, these are from my phone so they of course are not the best quality.
The Mount Vernon website is full of information about the house and I would consider it one of the premier museum websites out there. There are all sorts of education information, trip planners, and even a virtual tour of the mansion. Check it out at http://www.mountvernon.org/