I assumed that David's room was below the tower room. The windows in his room are similar in design and placement to his room being in the tower portion of the house. The shape of the room also would lead you to believe that was in the tower portion of the house. However, when they referred to the Tower, they usually referred to the Tower Room, meaning the top room in the tower and what was below it was never mentioned.
From the 1795 segment, we learn that what is David's room was to be Jeremiah's room and that it was the first door on the right at the top of the stairs. If you say the stairs are in the center of the house, then yes that would put David's room below the Tower Room.
Frankly, because of major inconsistencies in the way the house is setup in the series and the real house, just looking at the exterior, I gave up ages ago trying to make the two make sense. It is just not possible. Given the location of the front door in relation to what they show as the drawing room windows (the one's with the lights one) it would be a fair walk down that wing and that is not the case. So years ago, I took the same frame of mind I have about Gilligan's Island having all they have for a 3 hour cruise and decided to just take it on face value and not worry about it making sense in reality.
Raholt