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

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 .

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 :)

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.