How to ask and Sign to a Contract to BIG clients?

Sounds like you are a talented person. Your talent is priceless, but in business there is always a value placed. You have a clear cost/fee for your service or time. For example estimate how many hours it will take to do the project and multiply that by a numerical money value. E.g 8 hrs x $20. or quote a flat fee for the project and stick to it. Ask for a scope. If you feel client won't pay you, ask for money in advance. It's your business and there is nothing personal. Don't be afraid. If Bill Gates was afraid, there wouldn't be a Microsoft today. If after talking and negotiating with the client, and there is no compromise, let the client know that you can not work. don't waste your time. Time is money.