For what you’re doing I’d just get a 12’ tandem with brakes on one axle. Most any trailer dealer should have it in stock. If you get a custom trailer and decided you want or need something different, you’ll have a hard time selling or trading it. There was someone that had a very short car hauler for sale on craiglist forever that was too heavy to use as a utility trailer and not big enough to put even a small car or truck on.
Also, for your use, I’d get one with solid sides in case you need to haul sand or gravel and the ramps that aren’t attached that slide underneath. A fold down ramp makes it impossible to load anything on it with a fork lift.
If I was able to afford what I want, I’d have a dump trailer big enough to load my tractor on and a tilt bed car/equipment hauler.