What size is their fosse?
Quite right, some communes stipulate certain colour schemes, types of roof tiles, roof pitch, won't accept wood bardage etc. regardless of monuments historique - while others will accept anything, just depends on where you are and what there is to be "protected". If she's in an area where there are no restrictions - just look at any new build in the area and it'll soon be apparent - or as I said earlier in the thread, first port of call is the maire to see what the commune's attitude is - some (very few) are actually very accepting (more for yourtes but who knows!)
;-)
"appearance" rules exist if you are within 500m of a monument historique, otherwise you do what you like...! ;-)
Have you tried talking to the "HIPPY Couple"?
Anna I have sent you a friend request as I have some information that may be relevant to your post.
You can always have suspicions!!
Not a great deal you can do apart from having a word with your maire, if he wants them gone he may be able to put subtle, or not so subtle pressure on them, if he doesn't mind having them there you may just have to learn to live with them rather like the gens de voyage who build houses left right and centre then use all the garden for storing their caravans - they actually continue to live in the caravans and just use the house as a communal base... :-O
Unless it smells or blocks off light from rooms in your house, I believe the civil code does not have any sanctions for what people might consider eyesores. There may be issues over whether people can live in these structures, though. At least it is several hundred metres down the lane so it's not spoiling your view. Re tipping off the gendarmes about drugs, I know it was tongue in cheek, but I would not make false accusations as you could leave yourself open to a case of defamation of character!
Go the Mairie, they will be able to tell you can or not can do.
Good luck, it sounds awful.
(On second thoughts if that doesn't get you anywhere a tip off to the gendarmerie that they are "smoking" stuff could be useful).