According to Wikipedia, the name comes from a place in Rhode Island called Quonset Point where the buildings were constructed in the early 1900s. They were initially used by the military, but they became widely available after WWII when they were sold as military surplus.
Today, Quonsets have a variety of purposes, from agricultural buildings to man-caves! They can also function as prefab homes. You can buy quonset building kits for most any purpose such as garages and workshops. They're great because they're durable, and the arch panels are easy to ship and assemble. You can get a kit that's customized for the particular size you need, from a small art studio to a large space to work on rebuilding your vintage car.
Prices vary depending on size, etc, and the staff at Quonset Canada can answer your pricing questions as well as any other questions you might have about Quonset construction, use, etc.