The Mirror was designed to introduce the masses to sailing, with the chance to own your own boat cheaply. Many tens of thousands fulfilled their dreams by building a Mirror from a kit. Building a Mirror is not difficult, easy accomplished by anyone with basic DIY skills. These days many prefer the convenience and low maintenance of a GRP/foam sandwich Mirror.
The Mirror dinghy is an International Class, so it's class rules and licenced builders/kit manufacturers are administered by World Sailing. Mirrors can only be built from a kit supplied by a World Sailing Licenced Kit Manufacturer. Please see the World Sailing Mirror Class Page for the current list of kit manufacturers under the "Suppliers" tab.
The vast majority of wooden Mirrors were built using the original 'stitch and glue' method. In the 1990 some racing Mirrors were built on jigs that greatly help to achieve a good and fast shape. If you are interested in building a kit on a jig, here is Phil Rust's story of building GBR 70362 (using the Goodwin jig).