Who to talk to when a belligerent gringo ignores house construction rules

Municipio Obras Publicas or your local Government or both. Do you need a lawyer or will someone just come and talk to him

He has 2 second floor windows facing other properties and 2 slanted roofs dumping water in the lots next door

I know a gringo was ordered to fill a window in West Melaque because it looked into someones yard

Good luck with that. Our next door neighbor built what is essentially a four storey including a basement, ten foot wide building sans permits, including a balcony extending beyond the legal limit over the busy street. He was reported by more than one neighbor and a contractor. Would you like to know the result? NADA. Nothing has been done and it's two years now.
It appears that once a structure is up, no action is taken to change it.

The problem with Obras Publicas is they only want the money and only tell you what your foundation and castillos have to be. They want nothing on the permit about windows or roof. And they don't come and check

Here at least someone had to fill a window that looked into another yard.  Nobody but this jerk-off would dump roof water into other peoples yards.  He claims he's going to build gutters but has done nothing in a month.

He built a shed 2 years ago and aimed the roof at my back wall. Last year he said he would take it down and didn't.  I reminded him 2 months ago and nothing.  If he heads back to Canada this year without removing it .... I will gladly knock it down myself.

This jerk is exactly the kind of person that should not move to Mexico

When we lived in Mexico we bought a condo across from the ocean in PV. Six months after our purchase they started construction on a hotel right across the street from us. They put up four buildings, each sixteen stories high and only five feet from another existing hotel to the right of the one going up. The people in the existing hotel were really angry as some of the rooms on the side facing the new building were timeshares and now faced a wall of concrete, sixteen stories high instead of an ocean view. The neighborhood. and the existing hotel, did a lot of reporting on the new construction but we were told by the Reglamentos that nothing could be done. When we lived in the Chapala area we were warned not to buy near a vacant lot as the zoning laws were so lax that we could end up with a machine shop next to our home. It seems that payoffs can be powerful and most complaints about people abusing construction rules go nowhere. Of course, because this is a gringo who is making life miserable for his neighbors, you may get someone to listen to your complaint, but don't hold your breath. Beware when buying and building in Mexico. Been there, done that, it was not pretty.