There’s a few Arduino and compatible WiFi shields on the market, each with varying levels of success (and failure). This has led to many people seeking alternative hardware solutions to getting there Arduino project connected via WiFi, and one fascinating option has been documented by Arduino forum member “jft2”.
Here is the Link to make simple WiFi shield.
Blog : http://www.freetronics.com.au/blogs/news/10467653-make-your-own-arduino-wifi-shield
Reference site : http://forum.arduino.cc/index.php?topic=201294.0