I wouldn't water time or money or risk the horse's safety by building "cheap" - winter is when you get high winds, heavy rain, and thick snow weighing down roofs so that's when you need the good quality buildings! Better off building once properly - buy cheap, buy twice.
My husband said the same thing just tryng to figure out what wood, how big etc.. all very confusing have you ever build one? What di you use?, someone told me pallets but personnaly i think thats stupid as not strong enough for anything other then injuries which i dont want that
I use "4x2" timber for the frames, "6x2" and "4x2" for the roof and "6x1" for the cladding. I leave small gaps in the cladding, similar to Yorkshire boarding, to allow for wind loading. Even though the timber comes pre-treated, I still spray it with Ronseal Fence and Shed stuff to give it extra protection from the elements and insects.
I build each wall section separately using 6x100 screws and then connect the sections together using M10 and M8 coach screws. You can also use bolts, but I prefer the cleaner look of the coach screws. I don't really know how to build "cheap", so I build it to be strong and I use good quality and relatively pricey screws (Spax), but that way I at least know that when I want to fix, or take it apart, in a couple of years, then the screws will not have rusted and disintegrated. I am also sure that this thing won't fall apart on the windy days that we get a lot of. I have seen some of these cheap (£1000-1500) pre-made field shelters and have not been impressed. One of the neighbours got one and it needed extra timber to reinforce the walls, because it was so flimsy.
Even though I get a really good discount from the local merchant, the timber still works out to be quite expensive. I haven't done proper calculations, but I reckon that the timber, roofing and fastenings cost about £1200 for this field shelter (3.5 metre by 3.5 metre). Then you have to consider the time cost of the labour when doing it yourself, but after doing a couple of similar buildings, I can do one of these in a couple of days. Finally, you need to account for the cost of stuff that you may not have, or be able to borrow. For example: to put this thing up you will need G-clamps to hold it together before you can screw it together. You would need about 8 to 12 of these and the cheapest ones go for £6 pounds each. I also use a large folding square to make sure that all of the angles are 90°, like this http://www.screwfix.com/p/forge-steel-48-aluminium-folding-square/69436.
If you don't have the right power tools, then you would have to purchase them as well. At a bear minimum, I would recommend an impact driver and a circular saw, but if you have a lot of patience, you could get by with a manual panel saw.
Moving the sections to where the field shelter will be (the tractor is not compulsory)
Putting it all together
A close up of the joins - I probably could be using less coach screws, but I like to make sure that everything is firmly held together. I weigh 220 pounds and I can climb all over the frame without any issues.
The roof is on and I have started the cladding
Then I built a hay feeder out of the timber I had left over (still needs painting to finish it off)
I went to our local timer yard, spoke to the guy on the desk for a few moments telling him what size I wanted, how exposed the field was and he did the rest. He did a quick sketch, priced all materials and gave me a quote.
Less a roof it was around £608 if I remember, plus VAT, for a big 2/3 horse affair.
For a timber merchant it shouldn't be an unusual request?
For a cheap fix that won't fall down you could use mammoth straw bales and a tarpaulin. They do flap though and need anchoring really well or become a kite. Considering bales are £30-35 each probably not so cheap really?