I had my barn built in 2012. It is a metal framed, metal building because I live in Texas and termites are the devil.
My stalls are 12x14 and I LOVE the size! The layout is feed room/stall/stall on the right. Tack room/stall/stall on the left (left and right are as you walk in the front doors of the barn. I think some “must haves” in a barn are going to vary by geography. In hot climates it is nice to have tall ceilings with some kind of air escape. I regret not having my builder put in a roof vent. My husband later added a mechanical vent that automatically goes on when the temp hits like 100 or something. The roof vent would have worked better.
The 2 stalls on the right side each have a 15’ (ish) x 55’ run. One stall on the left side has the run, the other one goes out into a small paddock. I LOVE LOVE LOVE my stall/run/paddock set up. LOVE. Having the runs means that if one horse gets hurt and needs to be kept up, I can keep the others in also and they won’t go stir crazy. They can also stay in during inclement weather and still be able to move around. The extra bonus is when the horse figures out to poop and pee in the stall run, but not all horses figure that out (I’m looking at you Simon!).
A non-negotiable for me on this and any future barn I were to have would be gutters. Being able to control where the roof runoff goes is huge and gutters don’t cost that much. Plus it addresses the mud problems others mention.
I put swinging feed doors with built in feed pan and hay mangers. I wouldn’t do that again. I hate them. I would just have a swinging door to drop feed in as needed. I feed mine off the ground.
Also because it is hot, my stalls each have a ceiling fan. This helps keep the stall cooler and it helps with flies. I wouldn’t necessarily add ceiling fans in a northern climate, but they sure are nice.
Lots and lots of power outlets. You can never have too many! I put mine close to eye level and I like them at that height.
My rooms and the surrounds of each stall are concrete, but the actual stall floors are a rock base, then sand for leveling, covered by mats. Easy to clean. The concrete frame prevents the mats from moving. And the horses have plenty of cushion. I like the concrete aisle and in the rooms for ease of cleaning and attempting to reduce the amount of dust. I have mats in the aisles.
My barn has a 12’ porch on the front and I adore it. It has 3 ceiling fans with tons of lighting and it absolutely helps keep my barn cooler during the summer months. Eventually we will finish out one side of the porch to act as a wash rack with hot/cold water, electric outlets and other grooming/wash stall necessities. I didn’t want my wash rack inside my barn bc it gets humid in Texas and I don’t need that humidity in my barn.
Other nice-to-haves is that my barn aisle is tall and wide enough to drive a tractor/pickup into. I’ve parked my truck and trailer in the barn aisle during hail storms. My stall runs also have gates wide enough to get a tractor in to clean them.
I prefer my tack and feed stuff be kept in separate rooms to cut down on dust. Both of my rooms have heat and AC.
My barn is near my house so we didn’t add a bathroom or laundry, but there is a commercial stainless sink in the feed room with hot and cold water. We will be adding a 75 gallon water tank in the feed room to store water for the 7 days it freezes in Texas and we have to shut the water off to the barn.
One other thing we didn’t do that I feel like most barns have is the drop ceiling on the rooms. My rooms have 14’ short wall ceilings. The wall just runs up. We are adding some shelving up high in the feed room to store things that aren’t used often. Every drop ceiling I’ve ever seen is a terrible fire hazard for all the dust they collect. And the super tall ceiling makes the rooms feel fancy and huge.
Good luck and have fun!!!