Here is my easy DIY Single wheel bicycle trailer. It took about 2 hours of work up to this point where the drop out legs were installed.
Step 1: The Wheel Assembly and Cargo Area.
I used the fork from a small childrens bicycle for the wheel assembly. I found the bike on the side of the road. The one good wheel and the fork where used. I used the hole through the Y of the fork (most bikes have this) and bolted it to the cargo frame I used a 3 inch u bolt to hold it and the other end of the fork. this took no time to assemble.
Step 2: Making the Tongue
I used a 2x3 3/4 the length of the cargo frame for a tongue. I screwed it in using appropriate length screws. I cut angle 1x2 pieces to add support for sides from tongue. I drilled a hole for the pin to attach to my custom made pull behind bicycle Reese hitch. Its important to have a strong tongue that has no roll or left to right movement or shift. My hitch has a lip to slide the tongue on and drop the pin in. I made it so it can be tightened to help heavier loads. The 2x3 fits super snug as it should to have good support and balance. I added some small simple sides from salvage wood. The sides are a must to hold cargo in good.
Step 3: Adding Drop Down Support Legs
I simply used 1x2 wood cut to size. I used 1x2 framing brackets and a pin on each side to attach the legs which are just wood blocks. I am thinking about using a long bolt on each side through the bottom to make the legs adjustable in size for rough ground. It stands plenty strong to load and unload. The legs are easily spun up and strapped in place for traveling. This is my progress so far. I plan to paint, add hooks for strapping and a tarping system to keep cargo dry.