First, think multiple use and portable.
What you think you want now WILL change once you build and you will want to make changes over time to accommodate all kinds of current needs.
You may want a backyard barn for a few pet horses ridden in the weekends, a breeding barn that fits broodmares and youngsters, a low end training barn, a high end one, change disciplines and so needs in a barn.
CHANGE is the name of the game of life, build with that in mind when it comes to permanent structures that will be there for decades.
Our big barn can be used to store big machinery agricultural goods, is a horse barn with stalls and arena right now as it is intended to be training competition horses.
We built a shell and then all else added is portable, the stalls are, the run panels are, the arena panels and roping boxes and cattle pens at the end are, etc.
The tack room/office/lounge/bathroom and feed room are not portable, but they would be easily remodeled if necessary.
The barn is all metal, no wood on it, as in our area we have 100+ old metal barns that are still like new, we have several, all sizes.
The ones that were built out of wood clad with wood or metal all died eventually.
The portable stalls and panels lining the arena and roping boxes are metal, so is all other in there, except the human quarters, tack-feed etc, that are stick built and insulated and have a mini split for heat and air conditioning. There is a large window to watch the arena from that space and the bathroom has a shower and is handicapped accessible, etc.
We have held small agility dog shows in there and horse clinics, the local 4H trained out of it, but is a smaller, family oriented barn, not a commercial one.
There is so, so much to consider, location, orientation to catch best sun to dry things up, use wind to your advantage to cool in the summer, build so you can close the North side exposure off in the winter, if you get snow, build where snow will blow by, not make huge vortex drifts up to the roof that may collapse it, happened to a neighbor’s barn, has been reconfigured since.
Any kind of structure can be made also esthetically pleasant with a little creative thinking, some architectural details that don’t add to the cost, are built into the plans.
Think about what you will put outside, we have a french drain for the washroom and is a rock feature on that side of the structure, looks nice and finished.
There have been whole books written about how to build horse barns, check the library.
Above all, make plans for months, years if you can, keep pictures and lists in a file and keep adding to that and, in the end, once you have your barn, you will be so happy and also already start again learning more and what could have been a better feature, is all part of building anytihing.
Most important, if you wish, let others learn from your path to your perfect barn, so they too can dream of the one they may build, or use features to remodel theirs for better use or looks.
Oh, don’t forget to have fun, don’t let building stress you, buy a bushel of patience and use it.