How true is that!! We spend more time out there than in the house anyway!!
Good GOD, YES!!! I spent 5 minutes on my house and the rest of the time looking at the barn, the fencing, the shelter, the 4-car garage and the outbuildings!!!
Right above above stall size. I recommend the smallest
for a 15-16hh horse is my smallest stall, 8'x'12'.
I made stalls in my barn, put down 3/4" rubber mats over the cement and I've been VERY happy with this. My horses have turnout every day possible, but can stay inside for a week during icy periods.
You need the size so that you horse doesn't get cast. All horses like to lay down in a clean stall at night. I've found mine down in "Nativity Position" when I've surprised them early. They need the stall room to brace and get up again.
I bought 4 round pen panels, one the gate and made a 12'x12' stall for my 16'3hh KMH. Although people will say do larger, you really only need THAT for a foaling mare.
I think you could use the materials you have already and start rebuilding. It looks like you could make 2 stalls into one, since the supports use the frame of the roof, OR, price panels, like I did and use those for the stalls and save the lumber from THESE stalls for other projects. Maybe keep one stall up to store the rest of the wood. Truthfully, horses need LOTS of fresh air and wooden panels cut the air flow.