Using the sway of my building to measure wind speed.

I live on the 20th floor of a 30 story building. Recently I hung a pendulum from my ceiling in an attempt to observe the sway of the building, as a proxy for how windy it is. Image here.

It works, but I'm wondering if there is an optimal length for my pendulum to maximize the amount that it swings. It seems obvious that the longer it is the better, but are there some local maxima that coincide with the harmonics of the building?

I can imagine hanging a pendulum from my finger, and moving my finger back and forth sinusoidally. It seems like for some length of the pendulum the force of my finger moving would be additive resulting in a larger swing, and for other lengths it would have a dampening effect. Are my intuitions correct, and how can I calculate this for the case of my building and my ceiling pendulum?