How can i build a community site?

Go through a few years of basic programming, engineering, and design, then hire a small staff.

http://www.talkingpixels.org/diggclone/index.php

That might help. Honestly, if you are asking this question you probably can’t do it. Get a good book on xhtml, css, javascript, php, and mysql. But you can’t click on a couple of buttons and have it done. You need to learn how to code if you want to do this.

What is the goal you are trying to accomplish? Before building anything, I’d make sure there is a need for it and that it will be worth your time. There are hundreds of Myspace and Facebook clones. If yours isn’t filling a special niche, it probably isn’t worth the time. Just my two cents.

Buzzdash is a site where you can create and embed your own FREE insta-polls. Another free site is NING where you can build your own social networking site and community. I suggest you build a NING and embed a Buzzdash for voting.

http://Polleverywhere.com is also a site where you can make insta-phone polls.

Just go to ning.com and get an account. At ning you can create your own social network without any programing. There are some other services like this but I can’t recall them at the moment.
You could also just use somethng like wordpress, drupal, or phpbb, and then just build on top of them.