Here are some photos of a homemade trailer we used for awhile to move round bales around our farm. My father had someone make it for him. When he sold the cattle, he gave it to a neighbor.
It was a simple design and worked really well. The way it operated was you would back it up to the hay bale so the back roller almost touched the bale and then stop, flip a toggle switch to lock the brakes, continue backing up until the trailer folded over the bale and the spear fell over the bale, pull forward to pull the bale into the cradle, then move it where you wanted. To unload, you would get off the tractor and move the spear back off the bale, get back on the tractor and flip the toggle switch to lock the brakes, back up until the trailer folded and dumped out the bale.
He used this with his Farmall Super A which did not have a 3-point lift only a drawbar hitch. Later he bought a tractor with a 3-point hitch and hay spear. Much faster and no getting on and off the tractor.
I'm not sure if this is what you had in mind, but it worked well for po folks on a farm.