I got some news for you. The Mexican president is not in charge of whether the US builds a wall or not.
Of course. The article states that he won't pay for it.

He's not in charge of whether Mexico pays for it or not. All that the US has to do is place a small fee on "Remittances" from the US to Mexico. That's the money all the illegal Mexicans here are sending back to their families.
So you see, this is really not very complicated.