Look out for an old plastic oil tank - these make great arcs for porkers/kunekune
There's a green plastic model with straight sides and a curved shape - that's the best one to go for
Cut a hole in one end for a door (about 2ft wide and 2.5ft high and leave a lip of 2-3inches at the bottom to keep water out) and drill some 10mm holes in the opposite end to provide ventilation, you'll need to wash it out several times with plenty fairy liquid and hot water to move the oil residue and cap the pipe openings on top (we use a roof slate with a stone on top).
Once finished you have a green plastic arc, with a floor attached which is super easy to roll to a new position. You can usually find the tanks on eBay, gumtree, local ads.
Good luck with the pigs