Walk around with a laptop, stop, click, repeat until you have enough data. Now you have a floor plan showing how good the wifi coverage is.

You have to supply the floor plan image, but it doesn't have to be very accurate, to scale, etc. As long as you can recognize what room you are in, and about where in the room, that is fine. you click there, and data is logged for that location. As in, scribble something on a napkin, take a picture of it, done.

Dependencies:

Python-wifi - reads wifi parameters and statistics, like signal level. http://pypi.python.org/pypi/python-wifi

wxPython - in particular FloatCanvas for pan and zoom.

Python-numpy - Numerical Python adds a fast array facility to the Python language

Python - glues it all together.