Have you seen moldings in tiny or small houses?
Moldings add vertical interest between walls and ceilings of all types. They also eliminate monotony from similar materials and colors. Most importantly, they offer a subtle, finishing touch.

See the traditional white crown molding installed in this welcoming entry area. The tiny cottage is based on Whidbey plans from Tumbleweed Houses. (At Home Arkansas)
One rustic treatment caught our eye because it’s not a true molding. Instead, barn wood is installed like a formal picture frame around the ceiling — and creates a smart transitional impact.

Brownback wood comes from the protected, unexposed back of reclaimed barn siding. Milled pieces get used to define the ceiling here. (JC Woodworking, Houzz)
Whether you envision a modern home, cabin, cottage, bungalow or other style, there are many molding options. Start looking up for your downsizing inspirations, even in larger places. As a reference, below are some classic shapes.

Architectural styles call for different plane, concave, convex and complex molding shapes. In tiny houses, moldings are possible on a smaller scale. (Classicist)
More information: Molding prices vary depending on whether you pre-purchase or make them from scratch, plus installation costs. To see some of the steps, check out Fine Homebuilding or DIY Network.