I started off with a very inexpensive trailer which I bought from a boat repair company. This trailer would have been destined for the scrap yard in another few months given the state of rust. I had origionally bought it only for the axles which would have cost more than I paid for the whole thing. But after talking to a few people who knew about steel, I was told that the trailer could hold up to the 4000lbs with some rienforcement. I was expecting to put on it about 3500lbs and so this sounded safe.. As with the entire project, my main focus was (1) Reduce, (2) Reuse, (3) Recycle.
To that end, I spent weeks looking for the larger pallets which would provide lumber for raw material. Yes there was a Home Despot only one mile away, but then I would have been supporting deforestation. Instead I found a number of places that discarded 12ft long pallettes, which was the only common pallet size longer than the 8 feet I expected to need. I recovered roughly 3-4 regular pallettes, and 3 heavier pallettes built of 4x4 timber which I used in the south wall. In addition I found huge amounts of random 2x4 lumber, much of it older than I am. This caused some trouble later on, but often a single antique stud was as strong as two studs fresh from the mill.
What got the project off the ground was the contractor's in depth understanding of structural steel. He confirmed other advice that I listened to and we installed rienforcing steel at three points on the trailer. He then started the most difficult welding, and by the time we were finished I was doing a passable job myself.
By the time we finished the last welds, the trailer was noticeably heavier, but much stronger. Here is a shot of the trailer before the rienforcing at the back was installed.
This is what the roof looks like when the material is completely adhered. It doesn't look completely smooth, but after some more gravel and a snow coat everything will look great. Until the wings are finished, I installed a few pieces of aluminum along the edges to keep water away from the walls.