The conflicts and disputes always arise over the personal issues only
The drawback in this is that they have not entered into a proper registered agreement between them over constructing and sharing the common amenities.
It was your duty to properly enquire about all such aspects before purchase of the property
Now without knowing about the actual dispute between them no action can be taken by you in this regard.
In the absence of any legal dispute no suggestions can be rendered.
Alternately, you can consult a local lawyer and on his suggestion you may file a suit for injunction if he interferes in your possession and enjoyment of the property to restrain him from creating any obstacle or bothering you about your own construction work.