You are right. It makes a huge difference.I was amazed when I foamed my roof, and the underside of my house, that they closed up ALL outside air sources. The chimney effect was cut off. I have saved hundreds of dollars a year since then. You can go into my attic on a 105 degree day, and the attic temps will be in the high 80s.The roof decking is COOL on the underside. This technology is upsetting the applecart about everything we know.The theory is that most attics cooked from the heat buildup on the UNDERSIDE.My attic now feels air conditioned on really hot days.
With chickens, it gets a bit more complicated. We need to exhaust ammonia, and warm moist air.A cupola with a sealed attic above, and a vent below, seems to be the ticket.This will supply a heat release source in the summer also while the roof stays cool./
Many of the commercial buildings that we build are done similarly. Not necessarily with spray foam either. The gable roof above the attic space for the building I am building has R30 insulation directly applied to the roof sheathing (which in this case is metal decking on metal truss). Above the insulation is a gypsum product (for other reasons), ice and water shield, then the metal roofing. The roof is not vented.Doesn't need to be for this assembly.
There is not a one size fits all for all assemblies. Building science and theories actually have a bit to it. The industry is constantly evolving. Some is due to good sales efforts by different manufacturers etc.
The largest threat (not necessarily the only threat) to the deterioration of the roof substrate is condensation. When the air in the attic is cooler than the outside air etc. For example when a warm wet front moves in. Condensation will build up under the metal panels and drip. The venting or separation of the roof panels lessens this because it equalizes the temperature under the metal panel to that outside. Another solution is a vapor moisture barrier. In the case of the spray foam insulation, it is not necessary because it has it's own water resistance. In the assembly I have put together on my project we have ice/water shield applied over the gypsum panels.
Cupolas are great on their own. They are even better with bottom ventilation. The draw the cupola has draws in cooler drier air on the bottom and creates it's own current. This draw is more effective when it is not only pulling out, but pulling fresh air in at the bottom where the birds are.
The longer I live in the South the more I realize the best solution is open pens with a wind shield.