For the last year, I've been using a 3x3 grid cage with a grid top to let the girls graze. It's zip-tied and the top is all connected by grid connectors and it had a center support. It is not intended to be animal proof, but I figured it was adequate to keep them in and slow down any hawk that thought it found dinner.
The design has several drawbacks: it takes time to set up and take down; it is bulky even when collapsed; its hard to catch the pigs since the majority of the top grids were connected directly to the walls. Anyone who has worked with those grid connectors knows what a pain they are get on or off the grids, especially if you're in a hurry. I wanted something that had a quick setup and was still relatively compact so I could bring it indoors or throw it in the trunk of my car. Which meant losing the connectors but somehow keep the rigidity that the connectors offered. I also wanted a narrower cage so I wouldn't be required to run laps in order to catch a fleeing pig.
The sides remained zip-tied together, with connectors on the corners (it helps square the cage and the lid tucks under them). I added hooks to the PVC, so they hang off the walls on the inside of the cage. This helps keep the cage square and supports the lid. The lid is one sheet of 10 grids, all zip-tied together. A few binder clips help keep the top in place and prevent it from collapsing if something lands in the middle of the grids. The new design is still not animal proof, but the cage is always in view/earshot.
The sides compress to a stack of grids, the top collapses to 2x2 square (and I'm sure I could stack it to a 1x2 pile). The two pvc squares weigh nothing. The whole thing can be hauled outside and set up in less than two minutes and taken down just as quickly. Success!