I built a 6 stall barn and am currently adding another 20 feet to one end of it, total cost less than $200. I did purchase some of the 4x4 support posts but most of it is built of either pallets or pallet wood. I took several pallets apart to use the 2x4 centers for crosspieces etc. The walls are pallets with re-cycled tin on the outside and some recycled panels on the inside. The roof is re-cycled tin.
I started by locating a barn that someone wanted torn down and that is where the roof rafter lumber and the longer pieces of wood came from. That is also where the tin came from for the roof and outside.
You can use pallets but you must either cover them or go over them carefully and take care of any nails that are sticking out or splintery boards. I was very lucky that most of the pallets that I got were in very good shape and made of 2x4's and 1x6's I took the smaller ones apart, took the spacers out and nailed them back together to build gates.
Pallets are very hard to take apart without tearing them up as they are almost all nailed together with ring-shank nails. It can be done with a nail bar and patience.
I was also very lucky as I work for a company that sells laminate flooring that is shipped with laminate panels over the top of the pallets and they gave me the laminate panels. I used the laminate panels on the insides of the stall walls and on the dividers. They are smooth and easy to clean and the horses don't try to chew them.
You can build a very nice barn with not a lot of money but it is a lot of hard work pulling nails out of used lumber and sealing the holes in the used tin. Also taking apart the old barn and hauling all the materials was not easy.
I had to buy nails, screws, hardware for some of the gates, and a lot of caulking but none of it was very expensive. I have learned a ton about construction while building this, I know to make sure everything is square and level and to make sure I have plenty of crosspieces in the roof.
I am not a youngster, I am 48 years old and if I can do it, anybody can.
Mary