If you have a table long enough, or a table with a long piece of plywood on top, you can build a 2X9 open cage with that box from Target with the last single grid available to be bent into a hayrack. If you want/need a cage that large, and you want it closed, your best bet is to build the cage walls from the grids and go to Lowe's or Home Depot to buy two length of 16" deep wire closet shelving. Have them cut the shelving 2" longer than your cage, put the little rubber tips on the cut ends, and cable tie the flat edges in several places down the middle to hinge the lid. You'll have the curved edges curving over the front and back of your cage, and you'll be able to lift the lid from either the front or back of the cage to access your pigs.
And yes, OSUCavies, zip ties are our friends.