If your budget and your backyard are big enough for a Modern Cabana, then consider us extremely jealous. According to the San Francisco company's website, the structures are designed "around the premise that adding space should be simple and affordable yet look fabulous."
There's a range of floor plan sizes from 100 to 1,000+ square feet and the Cabanas can be insulated and wired. The kits come with pre-assembled panels, and the whole thing is meant to go up quickly (days, rather than the months that add-on construction entails). Permits aren't usually required, but it's probably wise to check your local codes and regulations.
The Modern Cabana website allows you to select features and get a price. The smallest size on the website, 10x10 feet, will set you back about $12,000. Sure, it's not chump change, but it's cheaper than hiring an architect and a contractor to build an addition to your house. And that's sort of the point.
In our dreams, our Cabana has bamboo flooring, French doors and air-conditioning. We'd use it as a home office or craft room. What would you do with your hypothetical Cabana? Artist or yoga studio? Play area for the kids? Guesthouse?