Recently I built my own bike trailer. It was a fun project that didn't cost me very much at all. I built the main frame out of bamboo. Here are some of my thoughts about the process of building and whether I think it is a good project to consider doing yourself.
I got the plans for this project from Carry Freedom. While the plans can be modified to use many different construction materials, I choose to use bamboo. Bamboo is cheap (or, in my case, free), readily available in many countries and has a great strength to size ratio. The Carry Freedom website has the information for obtaining your own set of plans.
I am currently living in a foreign country on a temporary basis, therefore, I don't have any of my own tools to work with. I borrowed the expertise and tools of a friend and together we build the bike trailer. We probably put between 15 and 20 hours worth of work into the project. There are portions of the job that require two people. Having an extra set of hands for the whole process is helpful.
Bike Trailer Materials
Bamboo: The bamboo we used for the project was bamboo that I found discarded from a theater production. I don't know anything about bamboo, but my friend who helped me build the trailer said that the bamboo I had wasn't the best quality. Apparently there is some bamboo that does not splinter and is more flexible before. However, my bamboo also wasn't the worst quality, so we used it.
Since we did not purposefully go out and buy bamboo for the bike trailer, we were limited on our choices of size. The recommended size is somewhere between 1" and 2" in diameter for most materials. I think that the main frame arms should be closer to 2" for bamboo. They should also be approximately the same size throughout the frame. Our bamboo ranged from between .75" up to 1.5".
Metal: This is where we deviated from the plans considerably. One of our design alterations was a good choice because it was material that we had handy. When constructing the bike trailer we needed a way to attach the wheels to the trailer frame. Instead of buying, bending and beating sheet metal for our purposes, we used 1.5" angle iron for the wheel dropouts. This worked very well because we already had the material and it saved us from the more precise cutting and bending that the plans recommend.
Trailer Bed: We ran several lengths of bamboo across the bed of the trailer. This provides the support needed for the wire mesh that is on top of the bamboo beams. We bought a piece of mesh at the hardware store. I am not sure what it is called, but it has a Â½" by Â½" weave in it. I tied it down with plastic zip ties to hold it in place.
Wheels: We tried to work with a set of wheels that my friend had lying around the house. Both were rusted through and not worth the effort and time to try to repair them. We ended up with donor wheels from a bicycle builder friend who has plenty of parts. The wheels are 26" wheels, which is the same as the bike. It is recommended that the bike trailer wheels be the same size as the wheels on the bike.
Bike Trailer Construction
When starting the project there were no firm plans on how long or wide the bike trailer should be. The plans I got from Carry Freedom did not specify a recommended length or width. My trailer ended up being about 2.5' wide by 3' long (not counting the 2' arm that attaches to the bike). It is wide enough to fit three wooden crates that we get from the fruit stand. The primary purpose of this bike trailer is for grocery shopping. We can easily carry a week's worth of groceries in these three crates.
The bed of the trailer was built first. We did not pay as much attention to leveling the trailer as the plans called for. Instead, we only worked on making it square. We did this by running a wire from corner to opposite corner on 2 axis. We then tightened the wire until we had the trailer square. We did this on what ended up being the top side of the trailer. Had we done it on the bottom, we could have left the wire as it was; but, we needed to cut the wire because it interfered with the deck we were building. The lateral bamboo sticks gave the bed its main form. Then we ran two diagonal pieces on the bottom side of the bike trailer which keeps everything square.
While the angle iron, which were the dropouts for the wheels, were easy to work with, we did not get them perfectly in line with one another. A lot of care should be taken to align them as much as possible. This will make aligning the wheels easier.
Bike Trailer Conclusion
I think you can certainly get a good commercial bike trailer that will do what you need. Connecting them to the bike is going to be easier. A commercially built bike trailer, like a Burley Bike Trailer, will cost much more, but the quality of construction should be better than what we were able to achieve, especially if you are considering using a trailer for a bike tour.
Would I recommended people build their own bike trailer? Building mine was very inexpensive. Because I got the bamboo free, the wheels were donated and labor cost me nothing, this ended up being a very cheap project. I spent about $20 for bolts, wire mesh, zip ties and inner tube. But if you had to buy everything new such as wheels, tires, bamboo, sheet metal and bolts, you are easily talking $100. For that price you could have a commercial trailer for just a few dollars more.