I wouldnt dob a neighbour in for something minor, and believe live and let live .........but a building of that scale to me would worry me - it would suggest their approach to 'authority and society in general' might also cause neighbour problems in the future.
Alarm bells also rang about the garage/stable combo - down in home counties where we used to live the standard traveller ply was to build stables 'for the osses' - always brick, oddly, with windows etc .....and then move in and extend and then take 5 years odd and hundreds of thousands of council money to fight to get them out again. In green belt, flood plain etc etc.
Sooo, I would possibly be dobbing them in for something of this size, since if this is the start, where will they stop.....