Let's say the guy down the street is a sucker for all things medieval. On weekends, he dresses up in armor and whacks other armored men with clubs. Sometimes he even jousts. You get the idea. Now let's say this same fellow wants his home to reflect his passion. He plans to encase the place with faux stone, and erect two tall towers on each flank, to make it look like a castle. He's within his rights to do so, right?
Well, the answer is no—if he lives in a condominium complex and his home is governed by a homeowners' association. Condo boards and homeowners associations have stringent guidelines regulating what a homeowner can or cannot do on a given property, for just that very reason. There are rules and regulations about types of plantings, grass, shrubs, or trees prohibitions against erecting flagpoles, installing signs or fences, or placing ornamental decorations in the front yard. You can't paint your townhouse chartreuse or magenta, even though you may love the color, because that would violate the aesthetics of the community in which you live. And you certainly can't go around turning condo units into medieval castles with turrets and coats of arms.
That said, condominiums are not Soviet police states, either. Some alterations and renovations are allowed, pending board approval. It's just a matter of figuring out what you can do, and what you can't.
Individual vs. Collective
In New Jersey, condominiums can be high-rise buildings (as in Jersey City and similar urban areas), low-rise buildings (likewise), vast townhouse complexes (the suburbs), or just subdivided houses with only a few units (Hoboken, to name one). What they have in common is that condominiums are made up of units, which are owned by individuals, and common areas, which are the property of the collective.
Generally speaking, ownership of a condo unit is limited to the space within the walls. The unit boundary can be the backside of the interior drywall of the unit's dividing walls or at the centerline of the unit's walls. The boundaries of a condominium unit are an important consideration at the time of purchase—particularly if you are planning to do renovations, whether they include installing a dishwasher or digging a moat.