I have two potbelly pigs i have recently just got. They are in a pen right know in the barn. I am going to build them a outdoor pen with a shelter. I am Building a16ft by 16ft for my two know. One is 30ib and the other 25. They are babies. What size of pen will i need for 2 adults,3 and four. We plan to get one or two more i the future. I am making the pens out of free wood palats and securing them in the ground with posts.