How to Make a Zoo in Minecraft

Building The Zoo

Build the base. A suggestion to do would be creating a 10 block by 10 block square for each mob's pen. Avoid counting any wall space. After all the pens are done, you could put little stands next to each pen, with Squidward or villagers.

Decorate the inside of each enclosure. For cows, you could put a plains area with a tree or two and some tall grass and flowers. For zombies/skeletons, you could make a cave and have water outside so they don't burn.

Build the walls. You can make them out of any material, but it's preferably at least one row of glass. For hostile mobs, you must make a roof or covered area inside.

Make your pathways. You can make them out of any material, such as sand or cobblestone, for example.

Adding The Mobs to The Zoo

Add mobs. If you are in Creative Mode, then you can spawn them. In Survival Mode, however, you’ll have to lead them to your zoo, and some will be impossible, like bats(1.4), squids, etc.

Enjoy. You could try to get Testificates to come by using minecarts or spawning them.