Hello,
I have not used it personally, but it has some very good features:
NetSpot is a software tool for Wireless networks assessment, scanning and surveys, analyzing Wi-Fi coverage and performance. It runs on Mac OS X 10.6+ and supports 802.11n, 802.11a, 802.11b, and 802.11g wireless networks. NetSpot uses the standard Wi-Fi network adapter and its Airport interface to map radio signal strength and other wireless network parameters and build reports on top of that.
It can do the following:
Wi-Fi mapping
Network optimization
Creating WiFi signal strength map
Wi-Fi network trouble-shooting
Wireless network visualisation
Wi-Fi signal problems diagnosing
Wireless network coverage analyzing