You know what,
Hello! My name is John Kern. The Best Software Engineer, Web Site and Web App Designer, Developer and Full Stack Software Engineer and Architect from Netherlands.
I stopped reading here. I mean how much one can praise himself? I mean if you were that good, wouldn't big names like Facebook, Google hire you instantly? There is a shortage of good developers in the world anyway. I'd love to see your GitHub

If only I had merit.
Also, you can't really guarantee an app/website WILL make money. Some things flop, and it's disingenuous to do so. I know you probably have the best intentions in mind/marketing, but still, that should be noted.
About Escrow I think we dont need that cause as I said I will work for free at first but we can divide the project and payment into parts and you pay me each time I get one part done. I will get the part done, then you will pay me.
So you're talking about milestone payments. That's not working for free. That's just working without being paid up-front.
Yes, you definitely save some risk on the end of the client, but that isn't working for *free* per say.