When we bought this place, it had this great, 36'X 75', fully enclosed barn, with 9-12'x12' stalls, a 12'x 12'wash stall with drain and a 7' high cinderblock wall on three sides, a 9'x12' tack room, a 'tacking-up' area of @15'x 12',and a 12'aisle the entire length-all except the stalls had rough cement floor. The stalls had all been 'yanked' out, water and electric lines cut, Nelson individual automatic waterers removed, because the place was to be repossessed by the bank. I designed 'do-it-yourself' stalls, and hired a retired carpenter to cut openings in the outside walls for dutch doors out of the stalls, and we built runs for each stall.
I am a HUGE believer in having outside access to stalls.If that's not possible, or feasible, I would suggest adding a 'lean-to'type roof, minimum 12' deep,( but 14' or 16', even better, for the best protection from the elements), to the outside of the barn where the stalls are, along the entire length of one of the long sides of the barn. The wall of the barn provides the backside of the shelter; add a roof, and if desired, a wall at each end, and you have a NICE big run-in shelter!This would provide the most 'bang for the buck', money and usable shelter-wise;you could invest in some portable panels that could be used to construct runs and/or a dry lot enclosure-which could be changed in size and configuration as your needs change, even using panels to be able to "shut" horses into individual 'stalls' under the shed when needed for individual feedings/overnight/ when weather is bad, etc. You could have horses in the available barn stalls, yet be able to accomodate a number of others outside. (I am a GIANT fan of properly-constructed-read:safe and sturdy- portable panels-they are SO versatile, enabling you to change as your needs change--AND, when you buy good ones, and maintain them, if ever you DON't need them, there will most assuredly be a good resale market for them, IMO.)
The foaling stall doesn't need to be that large; a 10' x 10', for minis, would be perfectly adequate-giving you another 10' x 10' stall. I agree with the person who said that your big horse could do with 'less' if he had a connecting run-but I might give him, say, a 10' X 12', and make a mini-sized 10' x 8',next to it, if that's feasible. For overnight stalling, that size would be fine, especially for one of your smaller ones.
Tip: Don't know how your barn is oriented, but would suggest opting for the "best" long side. For instance-my barn is oriented N/S; the stalls open to the EAST side--more protection from the prevailing westerly winds that way , and from the hottest afternoon sun. My run in sheds, though, are all oriented so that the open side faces south, so that the wintertime sun penetrates furthest into the shed(I have a 36' x 16' shed, and at the height of winter, the sun with hit all the way to the base of the back wall of the shed--surely helps with drying it out(from the moisture of peeing, and rain or snow that blows in!), and giving the horses a place to stand, feeling the sunlight, yet out of any wind, in the winter!) yet it is fully shaded in the summer. Just an added thought....
Good luck, no matter what you decide to do....!
