Although this issue is two years old, I will still add my 2c. First, I am surprised that the people who prepared the plans for your addition didn't verify the buildable footprint my refering to the survey. Maybe a professional didn't prepare any plans then I am wrong in that regard. Here in Texas we call this a Title Survey. Before a Title Company will issue a Title Policy, a survey needs to be prepared. You paid for this survey out of the closing cost. Somewhere in your title documents is a copy of it for your records. If you didn't get one, call the title company. You should have one. Preserve it. Don't draw on it. Run a few copies or scan it. Depending on how complex the addition is you can draw on one of the copies. Most surveys are drawn at 1" = 20'. So one inch on your ruler is equal to twenty feet. Depending on how sophisticated your city building permit office thinks they are, this should adaquate. Check with your zoning and HOA rules to be sure you are not encroaching on any minimum setbacks or easements. Anyway, I do hope by now you are enjoying your new room addition.