We used channel baffles, which take care of the roof ventilation issue. There are basic gable vents at each end of the structure, but they need to be upgraded. The front door (with a vent over the door) faces north, which is the direction from which all of our nasty weather comes. Given the fact that rain blows so hard against the front of the barn, I'm considering removing the gable vent and covering the hole, then putting in another vent elsewhere. This is a pre-fab storage shed like the one seen here: http://www.houseofstarsinc.com/id33.htm
Longer than the one in the #004 photo, but the same design.
ETA: Our structure is on a more solid foundation than the one in the photo. The previous owners intended to keep horses in it (??!!) and had that they called a "double floor" put in, and had even got two stalls built (even had the stall door hardware in place) before they noticed that there was no freaking way the space would work for standard sized horses. I think the full length of the structure is 34 feet. I tore down stall walls to create a 14x18 space for myself, and we're putting up a wall to separate my studio from the storage space in the back. I hope this isn't TMI.