Greetings Mr. Rudillas!
Although I'm not a contract grower myself, may I share with you what I've learned from my cousin on how to go about this business.
My cousin is a contract grower for one of the companies (I cannot mention the name of the company for fairness to other companies, I hope you could understand) and according to him you have to contact the company and talk to them about the possible partnership. From what I've gathered the company will provide you with the stocks, feeds and biologics and on your part you will provide the area (it should comply with existing environmental laws), labor and other necessary logistics.
The beauty of contract growing is that you are assured of financial gain at lesser cost on your part. And I think all the companies engaged in the business are offering these schemes to ensure their continued supply of chicken. Although in the first year of operation, don't expect to have profits considering that you will have to spend for the development of your poultry farm.
I hope this helps.