The dodger we had built for Spindrift (now owned by Frank) was made by Sperry Canvas in Marion MA. They might have measurements. The boat is on the small side for a dodger (both functionally and aesthetically) so having a template or an experienced canvas maker is a must. One challenge is that the primaries are fairly far forward so if you desire side protection the winch handle can come into conflict with the dodger sides. The optional dodger that came with the boat originally (see
https://jboats.com/j28-performance) had no sides at all. The dodger that came with our boat (see the large photo on the
j28sailors.org front page) had to be unsnapped or have the sides pulled forward with a bungee while sailing. When Sperry made us a new dodger we had them build in snaps so the sides could be folded forward and snapped out of the way when sailing. This worked well for us. As lines are typically led aft over the cabintop you will also need cutouts for those. In the attached picture the starboard side of the dodger is snapped forward and the port is fully extended. You can see the differences in distance to the primaries. People will be grabbing the main bar on the dodger a lot to get around the cockpit and down the companionway so it can be useful to have a different material there that is easy to clean and is durable and not afraid of fingernails. Sperry used some kind of faux leather trim material.