I have 12 X 16 run-in and 2 stalls (12 X 10). That was the maximum length of the pre-built barn I could order to deliver. Run-in is more than enough for them both to stand (and even sleep at night, which they obviously do looking at smashed poop and poop patches on coat). However they live together since I got them (number of years already), so they are OK about each other.
Here are some pics...
P.S. I don't keep stalls open (the bottom half), but we were in process of cleaning them therefore opened doors.
"Life isn't about waiting for the storm to pass: it's about learning to dance in the rain..."
"When we are no longer able to change a situation - we are challenged to change ourselves."
"How people treat you is their karma; how you react is yours."