This is the animal pen I created using the cyan nether wood planks. This is a 13 page set. I usually print the fence with an image set to 2 copies. But then they can get a bit small. So it is up to you how large or small you want your fences.

Some animals to consider for your nether pen are:

2muchvariety- https://www.pixelpapercraft.com/papercraft/5f2c9d135b61e1100c5459e0/strider-minecraft-116-nether-update minecraftisthebest2008- https://www.pixelpapercraft.com/papercraft/625b27f3763ddbb1e4a5fd10/skeleton-horseman minecraftisthebest2008- https://www.pixelpapercraft.com/papercraft/60ec75ffadd3a9250f251ee3/hoglin-minecraft-dungeons