Yes that's a good point, I'm not encouraging anyone to go on their roof at night, in fact I would heartily discourage it for the sake of safety. What I intended to mean was, I looked at Polaris at night, got the difference from the way my house/roof points, then took that protractor up to the roof during daylight to tweak the antennas. And as you also mention, a couple of degrees isn't going to make a lot of difference unless you are using some extremely narrow beamwidth antennas, so the fact that Polaris is actually about 2 degrees right of how my house points to the north is not of importance in my opinion. I positioned the antennas to point along the lines of the house and it works fine.
Jerry
The only problem using Polaris, or most any star for that matter, is that the only time you're going to see it is when it's too dark to go climbing up the roof or tower to adjust the antenna. I use the one star that is always visible during the day, the Sun.