Sorry, I'm not a code expert nor professional but I guess there is some resource of it on github, try to look for it for yourself. And with the idea of exchange I believe that it is a right choice as long as you do have something new to offer since most of the exchange does have their similarity.
THX,but I think if there is no expert on programming,the security of the site will be a big issue 
Yes, that will always be the main issue on each website that is being developed by programmers. Actually if you are not an expert the same thing with me, you can just simply hire out some developer/s out there that is willing to help with this type of project. You can offer them shares of stocks with your business or just simply pay them.