My neighbor has left his garage addition unfinished for years, when/ how do I complain?

I live in a cul-de-sac and the neighbor directly across from me abandoned his garage addition when his daughter moved out, as the bonus room above it would have been for her to live in. It has been over two years, maybe three. He has slowly covered it with plywood, adding a board or two every now and then, but no real work is being done. I talked to him once about it and he said he changed the permit since it would be unoccupied space, but I didn't think that meant he could leave it indefinitely. When I moved to this neighborhood five years ago it wasn't dumpy, but I fear this unfinished garage will deter any prospective buyers when my family and I decide to sell. I don't want to be unneighborly, but I feel like this needs to get fixed and I'm at the point of calling the city to complain and get him fined. My wife and I didn't exactly buy this house for the view, but it's hard to ignore and I feel it takes away from our quality of life.