Minecraft wiki entry for Animal_farming, associated text: The solid blocks can be switched around to make different designs. The only important ones are the grass blocks in the center.
This design has been tested with 100 sheep successfully but with that many problems arise. If some of your sheep are missing, they may have glitched through a wall or suffocated due to the maxEntityCramming gamerule.
Max time between harvesting: Unknown
Max number of sheep possible: Unknown
Max number of water levels you can create: Theoretically infinite
If you would like it to be wider, you can mirror the design and have two water bodies joining together. However this is the widest combination because you have to be able to control the water.