Source: http://lifehacker.com/5911812/share-your-internet-connection-using-an-outdoor-wireless-access-point
Early retirement weblog Mr. Money Mustache engaged in an experiment to see if he could share a high-speed internet connection with a friend 900 ft away—too far for sharing a Wi-Fi connection using his router. He purchased and installed two high-power wireless outdoor access points, installed them on each roof, and found a way to run an ethernet cable from their router to their roof. In his particular case he had to step up to a more powerful antenna but that all depends on your distance and if any trees obscure your line-of-sight connection.
You'll need to be savvy with how to manually set an IP address and be able to assign router DHCP Lan addresses on 192.168.2.x subnets, but you'll be able to share an internet connection with a friend saving up to $300 per year and means that you'll never have any problems getting a Wi-Fi signal in your immediate neighborhood. You can also use this technique with one antenna to fine-tune a nearby public Wi-Fi network that you can't otherwise pick up at your home, such as a citywide pay-for-use Wi-Fi network.
Finally, most for-profit ISPs have restrictions against sharing internet connections. Make sure you have carefully reviewed your service restrictions to see if this is allowed before attempting this setup. If you disregard the restrictions you can face fines or worse. For that reason we're tagging this a dark side post and reminding you that it is for educational purposes only.
Internet Sharing—How to Get Revenge on the Cable Company | Mr. Money Mustache