We recently decided we needed more shelter for some of our expanding herd of critters. This little barn built from pallets is working out well. The pallets form the basic structure. Over the pallets I tacked on a layer of cardboard to act as padding for the plastic agricultural film used as the weather proofing finish.
I started out by setting six pallets up on edge to form the shape I wanted for each arch. After I had established the angle that each set of pallets met at, I marked out a piece of chipboard to match that angle. Mine worked out with the bottom joint and the second joint being different from each other and the center top joint matching the second.
For the first and last arch, two sets of these chipboard gussets are needed. For any arches between those, one set is needed for each arch. I built the first arch laying down. After nailing the chipboard gussets on the top edge, I slide the gussets underneath the pallet arch and nailed down thru the pallet and gusset. This leaves the nails sticking out so be careful when raising the arch.

I only built the first arch laying down. The complete arch is fairly heavy and needs to be temporarily cross- braced to maintain it's size and shape while being stood up. Once up it needs to be leveled and tweaked to keep the sides parallel. I didn't pay enough attention to that on mine and had to fight to keep every thing lined up later.Several things to keep in mind when building with pallets, especially used pallets, they are not necessarily square or exactly the same as each other.While all the pallets need to be the same basic size, mine were all 40 x 48 inches, they did vary. Some had thicker or thinner boards, some were not flush with the frame.These differences have to be accounted for as you go. If you want easy and exactness, go buy lumber!
With the first arch standing and adjusted I nailed on my bottom row of pallets with the correct gusset between them. Add a piece of the same chipboard at the bottom so they are evenly spaced.After this bottom row is on, take the time to level and adjust so that the sides are parallel.
With the first arch standing and the bottom row lined up and secured the second row of pallets can be added to the number two arch. The third set of pallets to complete that arch are then put on. I tried to keep the outside of the pallets lined up and left any differences show up inside. There is a cross brace between the tops of pallet set number two to help prevent the arch from spreading under weight. Most of these pallets had hardwood frame members. Since this is difficult to nail through by hand I used a air powered nail gun.

If I hadn't had that I would probably drill and bolt the pallets together.Since I planned on covering this with a tarp or plastic film I knew I had to cover the pallets to prevent the odd nail or sliver of wood from pocking through. My first choice would have been some used carpeting but nothing showed up so I went with what I could get, cardboard. I tacked a layer of cardboard over every surface the tarp would touch. The tarp idea fell through so I bought a roll of heavy agricultural film.

This is the type of film used by farmers to cover bunker silos and is available in large sizes. While sort of pricey, it is strong and fairly durable. I do plan on recovering this in a couple of years with a industrial type tarp. Both ends are also pallets with a few pieces of lumber where needed. I had some used windows. There is one interior partial divider which greatly stiffened the structure. This formed the two pens at one end. We have had 18-24 mile per hour wind gust since it was covered with no problems.
The long edges of the plastic are not nailed but were left about two feet longer than needed and covered with 8-12 inches of soil. With about two tons of soil holding it tightly to the ground it should stay put. I nailed the ends and later also taped them with compatible tape.
We have our pigs and rabbits in here now. I did spend some extra money for rubber cow mats to surface the pig pens. Hopefully this will be enough to prevent them rooting it up. So far it seems to be working.
Here is mama "Petunia" with her litter of 8. They seem to like their new accommodations. We add some more bedding every day or so and they grind it up and make it fluffy. Now you can't see them in their pen when they are sleeping. You can hear them though, Petunia snores!
This project requires some basic carpentry skills and some physical strength. Pallets are not horribly heavy but they are awkward when you are holding them over your head with one hand and nailing with the other. I did this project solo but a helper would be advised if possible. I ended up with a 11ft.7inch. X 16 ft.8inch structure. Each arch was made from 6 pallets. I do not have plans but if you have a question I will try to help.