how can i build my own ptc site if i have the script?  

If you can use Dreamweaver or Frontpage than you can do it. Just go online, download a free template and use it as you wish. After downloading it you can either modify it or just use it as your source of inspiration to build your own design, as you will have your script to inspire from.

If you have a script, follow the instruction details. You will need to set up a database, afterwards run configuration files... its not that hard :)

I think you should explore some good tech forums for getting more information on such matters . Tech Forums are the best resource centers where many people are really helpful in guiding about the technical aspects . You will able to share your knowledge there and also gain knowledge from others .

You can also do a search and find out how others have produced their programs. Just remember you need a good business plan before implementing yours. Make sure you have enough funds in each account in order to follow through with payouts. The other is to know what your members are going to do for you and you for them to be able to earn as well. Make a forum of your do's and don'ts this way they can read it again in case they don't understand the TOS. They can read it in English.

I have seen different sites that you can actually get the programing/coding for a PTC. Probably just the basics, you will have to tweek it to fit yours.

There are also sites you can learn to do that with also.

Make sure you also abide by Alertpay and Paypals, TOS.

I hope it works out for you.

Most PTC scripts are easily hackable and full of bugs. geN4 from ptcpay.com is the best and most stable one. It comes with a guide on how to use it and an installer as well, not to mention free support!