One command - Barn on demand 'mod'

Moving mobs is one of the most boring and irritating things of Minecraft. 
That's why I decided to make this "Barn on demand" Vanilla mod. 
You right-click the spawn egg, and you'll instantly get yourself a 'barn', with most passive mobs.
it is no rocket science, but it is pretty convenient.

Make sure you do this in an open area, because I don't want to be responsible for destroying one of your buildings.

You can copy this command, paste it in a command block, power it, and the magic gets done.