Are the horses in good health? What are your winters like?

If they get along, and are in good health, I'd:

Very mild winters I'd put up some sort of hoop house to protect from LIGHT snows and winds and secure enough to withstand them. Horses may or not have an issue with the tarps blowing & the noise, depends on the horse, I probably wouldn't do it with a rescue.

Medium to heavy winter weather with any type of snows over 4" i'd opt for a walk-in stall to accomodate 3 horses at once- plenty big enough for all of them plus some for inside feeding ect. I might do this by building (we always have lumber around), or dropping a sea container (20 or 40 ft, like what they use for overseas shipping), or covering a carport & closing in the sides. I would NOT use a hoop house for horses if you have medium to heavy winters.

Cheap, cheap, cheap, temporary shelter I might make a secure lean-to against an existing building.

It really depends on how much money you are willing to spend. I was never one to do thing twice unless I had to, if it were me I'd plan for it being either permanent or for a conversion to something useable when the final barn goes in. For example, the carport can be covered fairly easily then used as the frame for a greenhouse later.

Figure out what you can do with what you have. It should be sturdy to support in your weather climate, sturdy to withstand a good kick from a horse, and solidly built enough that no hooves will go through it nor sharp edges to cut them, and enough space for you to maneuver for feeding & watering daily. Oh, and it should be convenient & on dry ground if at all possible.

Just some thoughts off the top of my head.

Brendasue

Hello! Been rescuing horses for years, so here ya go. Cheapest and quickest is to use panels to create stalls inside the hay barn. Or, if you don't have a pasture fenced yet, simply create a round pen using the barn as one side, with the barn being the wind block on the northside. Secure the panels to T-posts with chain to keep them in place if needed. Horses are usually fine with water, wind block and hay. Oh, and salt block. Get at least a 75 gallon water tank and tank heater for 3 horses. If the horses are old or ill, put them IN the barn or get blankets. But in any case, make sure to only feed them grass hay to begin with and make sure to use a water tank heater, both to help prevent any colic due to the changes they are going through. Good luck!

Mustang