Don't forget a large washing stall with the good rubber mats , hot& cold water with a hose wheel or a round wrack mounted on the wall
Also have a professional technical person connect up cameras in each stall as a " steady- on" mode for each stall so you can observe each stall at the same time inside your house in case something happens in the middle of the night. Do you remember when Roxy ( Stacy Westfall )was cast in her stall while pregnant and she couldn't make it, no I am not blaming Stacy , with horses anything can happen at a split second as I had a pony that opened up her gate and ran out on the busy highway and was killed by a big truck that could not stop in time. So if st all possible see about installing cameras for each stall, and maybe a sound monitor also. Your horses are your life and you give your ALL to them so you want to guard them and protect them all through the night.
A bathroom in the barn is awesome, even if it's just a toilet- it doesn't have to be fancy, just functional. Hot and cold water is also really nice. If your barn is somewhere that's wet for a good part of the year, a concrete floor is going to save you so much hassle (muddy aisles are the worst). Make sure you plan in storage for hay and bedding and feed (and again, if you live somewhere wet, covered storage with mats or a concrete floor is going to be your best bet), as well as somewhere for manure. The bigger the stall the better. My barn at home has 12x14 stalls and the horses love them. If you go with a metal building, realize you're going to have to insulate it unless you live in a very temperate climate.
If you're looking for companies, I've heard good things about King Barns as well as Morton Buildings.
Sorry if this wasn't quite what you were looking for haha.