You can see from the photo the fields I had to deal with when I decided to get my first pigs so if I can construct a pig pen on this slope anyone can do it!
I found that the best approach would be to prepare two areas side by side and fence them off from each other leaving a gap of approximately 7 foot in the centre of the two fields. The pig ark sits here but has doors which fasten at each end thereby giving you a spare field which you can rotate to when you felt the current field was due a rest. I tended to use the same field for 3 sets of weaners and then swap for the 4th pair. If you have a gate which opens into each area then it is two separate fields with an adjoining house! This system saved me lots of messing around worrying about preparing another area especially with the slopes that lie on our field I was sure that one lot of pig fencing was going to be enough! I have tried to choose a photo which shows the house in the middle and the fields either side with the gate.
As for the fencing I use 3 inch round 5.5ft posts knocked in to a depth of 2.5ft with a strainer post about every 4th post along to create tension. This is absolutely necessary with pigs - they will amaze you just what they can do with their snouts. I use galvanised pig netting and use the roll with the biggest hole at the top. You want to nail the smallest end to the bottom as this is where the nose will be most of the time. I use round 3" nails to secure the netting on every other post with the corner posts being supported by a strainer on each side. I also run a single length of barbed wire along the bottom of the pig fencing on the inside of the pen. This really does prevent your pig undoing all your hard work. A pigs snout is extremely sensitive so he will only bump into it a couple of times and he will know to stay away from your handy work!
My field had a stream running down one side so I have put in each side a self filling plastic bath it is specifically for having between two fields so it fit under the netting and there is a bowl on each side of the fence so they have water whichever side they are in. This is not a difficult thing to do provided you have a water source not too far away. I have simply used 3" connecting blue plastic water pipe from the stream fastened securely underwater back along the ground in a little channel connecting all the way in pieces to the drinkers and then an attachment allows both the pipe and the bowl to be fastened together. Provided my stream doesn't dry up then my pigs should be ok! It may sound daunting for those who have never done things like this before and there is no one who panics more than me when faced with a new task but all I did was go to the local agricultural suppliers and explain exactly what I wanted and the man came back with all the bits like magic - they have done it lots of times before so are a good source of guidance in these early months.