Decorations give (some give XP or extra house slots as well) over different periods of time, and some are purely for decorative purposes only. When you start your village there will be a few freebies. New limited-time-only decorations are usually available every weekend for special themed quest chains. Usually, building new decorations are part of new goals. Even though some decorations may be more expensive and give less profit than others, there are three factors to take into consideration when building new decorations. The first factor is how visually appealing it is. The second factor is how much area it takes up. The third and final factor is how long it takes to build.
Main Article: Common Decorations
Main Article: Rare Decorations