I had made mine using a 15" aluminium kuali and the sad thing is: I use it in my campus accomodation and the wifi access point is actually about 150m to 200m away and it is blocked buildings and also walls, although I pointed my dish antenna to the correct direction, it still didnt get any signals.

Material also taking into consideration if you making a dish antenna, for example a steel one may reflect better than an aluminium.

For those who have nothing or few things in between your antenna and the access point, you may happy with your work result.

How your ensure your DIY antenna is working at that frequency range?
Is there any formula or method to calculate them out for your own design?
How about if I want to design my own antenna for 802.11b and 802.11g?
Thanks

I tried, and it does helps a little in signal strength enhancement on my D-Link 7dBi antenna.