We have the double doors. To keep rain/wind out, the top door is closed and they can go in underneath the top door. If more ventilation is needed, both doors can be left open.
After Nicky's eye injury, he was trying to remove his eye cup on protruding edges, so we screwed stall mats on the walls--so they're kind of like horse rubber rooms. The inside doors have bars on the top, similar to Eagle Ring Farm's second photo. Nicky's next trick was to rear up and place his front hooves on the door edge to see where I was going whenever I left the barn. I was afraid he'd get a leg caught between the bars, so we cut pieces of stall mats, drilled holes in them and used zip ties to attach the mat pieces to the bars. The mat pieces prevent him from placing a hoof on the wooden edge but only extend up about another foot, so one still gets the ventilation effect of the bars.
The only comment I have on some of the other designs pictured here: Some of them seem kind of low to me.
On the first night we owned Coco, I locked her in the stall, but since it was a hot evening, I left the top door open for ventilation. I didn't know they could jump that high, especially with very little room to get a run at it. That's how she got herself pregnant... hopped right over that door (see photo with red arrow.)
To put it in perspective, this is how tall the lower door is compared to her (kinda' blurry, sorry.)
