How would you create a good mushroom farm on Minecraft?

What I usually do, is create a huge mushroom farm.

You can create one pretty much everywhere, even above ground, but under the following conditions:

• Huge mushrooms come in three different heights(5, 6 or 7 meters tall) and require a 7x7x7 or 7x7x8 area(LWH) to grow(per huge mushroom).
• The light level of the block that the mushroom will be placed on is 12 or below, unless placed on a podzol or mycelium block.
• At least 1 block of empty space must exist above the maximum height of the mushroom in order for it to spawn.

Another thing to note is that huge mushrooms will not grow above height limit(in case you one wants to create one in the sky for whatever reason).

Since getting podzol or mycelium requires silk touch and finding a mega taiga or a mooshroom island(most rare biome), you can just create one on normal dirt.

In order to create a basic design of a working huge mushroom farm, you need to do the following:

1. Mark a 7x7 block area.
2. Build an at least 5x5 solid block platform 8 meters above your 7 by 7 area.
3. Dig one block in the center, and place your mushroom there.
4. Repeat the pattern depending on your needs.

So, for example, if you want to create a farm on 50 meters, you need to create a 5x5 platform at 59 meters.

Use some bone meal to see if it works properly.

I re-tested this and it works at the latest snapshot.

Extra information on mushroom farming:

• Mushroom Farming
• Huge Mushroom

An alternative requiring a bit more work would be a mooshroom (mushroom cow) farm. The advantage is, of course, that you can theoretically have indefinitely many mooshrooms in basically any area - even a 1x1x1. (Due to the new collision mechanism in 1.9 and the general resources each entity uses, "concentration camps", as Antoine called them, are not recommended at all. I am just saying this alternative doesn't require a lot of space at all and bypasses the mushroom 'block' limit of 5 in a 9x9x9.)

The setup would be as follows: Have some breeder cows - imho at least 10 - which are never going to die. That number can easily be increased to fit your needs. [Pro tip: Keep the breeder cows in seperate pens with 2 cows per pen and have a contraption for the babies to get separated as well.] When the babies have grown up, use a shear to receive mushrooms and turn the cows into normal cows. If you wanna do something with the normal cows, fine, else just kill 'em for some beef and leather.

Quite obviously, you'll need to find at least two mooshrooms first, and get them to your base securely.