First, sorry for my english.

I have little ability to design a wordpress template and want to try to do a job from this one. After I surf on internet, I found a site I think exact with my concept:
http://premiumthemes.net or now http://templatic.com

I want to make a site with a membership system where only registered members can download my templates. There was also a referral system for those who want to help me selling my templates. Plus a page of templates free for download.

Because I still lay in the creation of affiliate membership site like this one, please give me advices who has experienced or has information about this case what must I prepared to make such site? Scripts or anything?

Previously thank you so much for your help!

If you have little experience, it would be best to hire a designer + coder to do all of that for you. You can alternatively look at some premade paid scripts at hotscripts.com, although you may have to do some code customizing to get exactly what you want.

where can i found the designer & how much it cost?

about templatic.com they customize wordpress for all their needs.
There few scripts in market to match your requirements like egbusiness (http://script4profit.com/egbusiness)

and about cost of a developer for custom solution it base on your needs, like you want whole site with shopping cart or only want affiliation/member system.

To further elaborate,
having a custom designed site with a working shopping cart(+payment system) with a member system on a professional scale would cost you thousands of dollars. There are many sites through which you can hire contractors, just search google. I would advise against hiring somebody that will do this for you for a 100 dollars. It would result in low quality work and sloppy design, something you definitely do not want if you want to make a profit with this type of a site.

If you're low on cash, go take some courses and read a lot about web design + coding + advertising etc. Then buy a premade script and tweak it yourself to suit your needs. Personally, this is probably the best route to take for someone with your level of knowledge on web design because even if you do hire a contractor to make a complete website for you, it takes specific skills and knowledge to maintain and expand a website of that nature.

Take my advice, if you're serious about this then take at least 2 years of time to learn everything you can first.

hmm...allright then. thanks alot for your advice!