My off-road POPUP did not come with the roof mounted air conditioner. I had that installed at the dealer as part of of my purchase. The dealer than cut the 14 inch by 14 inch holes through the roof and adds the boxing around the hole.
Then they add one or two ceiling support angles across the ceiling on both sides of the air conditioner install to give it needed support cross members. I don't think this is a JAYCO provided item and is done by the trailer dealers. Just like the batteries are not provided by the Manufacturer.
This google image shows ONE cross member angle where mine has two sections - one on each side of the air conditioner unit.
My install also has the wiring conduit like shown here for the 120VAC wiring cable to operate the air conditioner.
Photo shown from GOOGLE IMAGES
You can probably find what you need from LOWES... The best bet would be to go to RV Dealer that sells POPUP units and purchase one of their roof air conditioner install kits...