https://mobile.nytimes.com/2017/01/2...m.facebook.com
An interesting read but seems completely flawed if it ever is enacted.
In short it says Mexico won't pay for the wall, it would be companies that want their products shipped from Mexico to America will pay a 20% tax, thus American companies will pay for the wall.
Mind you I think the wall idea is a completely dumb, we could build a Bullet train or something revolutionary for The American way of life with that money instead of a crappy wall to keep people from picking our lettuce for dirt cheap.