I ride bikes........and I use bikes to work. I consider my bikes "working bikes". I only have pictures of a finished product and I will do the best I can. I have built and broken lots of trailers. It has taken my years to get this far and this one is not perfect either.
The solid weight I can carry will surpass the safe use of conventional V-breaks and I had 5 pallets stacked on it only to get a small bounce going down the road. (Tire pressure is everything!)
This is not my own design. I rode pedal taxi for years in Phoenix. This trailer is made from a hand truck and is modeled after a 3 passenger taxi that came from San Diego.
This main photo is on a "test" run (for beer!) and taken by myself.

Step 1: Get a Hand Truck.

This is a Harbor Freight hand truck with 10" wheels. Unfortunately, I started this project just before I found out about Instructables. I will do the best I can and will answer question.
I used a grinder with a cut off and grinding wheels, hack saw, tubing bender, drill, and a welder. Other than the hand truck you will need some 1/2" iron pipe, 5/8" iron rod stock, 1" flat washers, and various parts for the hitch. (in later steps)
1.I cut the welds off the center tube at the cross members and cut the tube itself at the handle where your hand goes.
2. At the bottom cross member cut the outer tube on both sides and you will have a large U with 2 cross members and some tube from the handle still attached.
3.Cut off the tongue of the dolly flush at the tire guards.
4.Use a tubing bender and bend the center tube to fit YOUR bike.(this picture is how I sized this trailer around the tires on MY bike (700c not 26"). Your situation will be and look different. The 1/2" iron pipe is used to size the distance to your hitch)
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Step 2:

1.Using the scrap U shape, cut off cross members and handle remains.
2.Cut the U down to fit in place to complete a level platform surface.
3.Cut cross members at angels and grind curves to fit as supports and tail light bracket.
4.Take out old axle and cut 5/8" rod to length. (My wheels are to the end of the tire guard.)
5.At this point you can weld it all up. Including: The iron pipe into the center tube, the axle to the trailer (so it does not rattle), and the 1" washers onto the axle for tire stops.

Step 3: Another Perspective

Just another view to help out.
Only one note on the picture.

Step 4: Hitch and Receiver

I used 5/16" nuts and bolts for the set screw system and steel tube for the hitch. The receiver is square stock with 1/2" flat washers added for pin wear. The reason I do not give sizes is due to the huge differences in seat post diameters.
1.Purchase your hyme joint first and fit your receiver to the diameter of your tube needed to fit the seat post. Leave room for hitch adjustment and a shim.
2.Cut tube for length needed for hitch.
3.Drill holes for set screws and weld nuts in place.
4.Mount hitch onto seat post (use a shim).
5.Determine the angel for your receiver and mark it (use the tube as a template on the top and bottom to get your angle).
6.Use hack saw to cut lines into your arc top and bottom and finish off the arc with the cut off and grinding wheels.
7.Weld hitch to receiver and washers to receiver.
8.Cut around the weld to get your right and left clearance for your hyme joint.

Step 5: Hyme Joint

Every place you go has a different name for a hyme joint. I got this one at Grainger and it is a 1/2" ball rod end. You may need to go to a specialty shop for this particular bolt because it's an odd thread.
The note about drilling a hole needs to be taken into account when sizing for the first step.
1.You will need to take your special threaded bolt and grind the head down to fit into the iron pipe. This can be done by putting the bolt in a drill mounted in a vice with the trigger lock on and using a grinder at the same time to evenly size the hex head down..........Its a good trick!
2.With the hitch mounted on the seat post and the tires back on the trailer, determine the length of your trailer (similar to the picture in the first step). Keep tire clearance of support bracket and up & down travel in mind.
3.Weld.
4..............?...???........Go drag it around!

Step 6: The Bucket!

I got a plastic barrel and mounted it with a single U-bolt in the bottom at center. I also used the tongue I cut off the hand truck on the bottom inside the barrel for 1 large secure mount.
I later added a bike rim to the top of the barrel on the inside rim (it needs to be a rim bigger than 26"). I can now strap a 8' ladder down. It hangs off the back but it is strapped to the trailer and as far forward as the hyme joint (almost) with a ratchet strap.