How to make a windmill in Minecraft:
Step 1: Find some flat land of suitable size, somewhere surrounded by grass helps the mill look more realistic when its finished. Although feel free to ignore this step and build your mill in a volcano.
Step 2: Start the base of the windmill by building a 10×10 square.
Step 3: Make this first shape 5 blocks tall.
Step 4: Seal off this first section with a roof.
Step 5: Decide which side of this box will be the front and build a door there.
Step 6: Remove the grass inside the first section and replace it with a suitable material for a floor. Wood will do but you can also experiment with different colored wool.
Step 7: Make a set of stairs breaking out of the ground floor section.
Step 8: Build up another two blocks all around your structure.
Step 9: Build a new box shape on top of what you already have with dimensions 8x8x5 (WxLxH).
Step 10: On top of this build a third box of dimensions 6x6x5.
Step 11: Finally build a forth box on top with dimensions 4x4x5.
Step 12: Carefully take out the corners of all the box shapes you've made so far.
Step 13: Replace these blocks with a darker material, unprocessed wood is suitable. This gives the windmill a nice detail and stops it looking like one big bland box.
Step 14: Position a few blocks coming out of the top of the mill, These are the blades will be attached to
Step 15: Using a colored wool build 4 symmetrical blades. Make them at least 10 blocks long
Step 16: Take out the middle section of your wool blades.
Step 17: Replace these removed parts with a fence post. This gives the blades a more solid feel and helps make it look more authentic from a distance
Step 18: Head back inside and build a balcony attached to the 2nd box shape we built earlier. Decorate this with items such as a picnic table and BBQ.
Step 19: Add a series of ladders leading up to the top of your mill.
Step 20: If you want you can add torches around the place to help keep it free from zombies at night or just so it looks nicer.
Step 21: Create a window from the 2nd box we build earlier looking out onto the balcony.
Step 22: If you have not already done so you can build some support columns form the balcony, These do not do anything apart from make the mill look more realistic.
Step 23: Head back inside and build the mechanism for milling wheat. The main components you need to create for this are a long shaft leading from the top where the blades are down to the bottom where you should put two flat surfaces to grind the wheat between. Unfortunately Minecraft does not have the ability to make large mechanical contraptions like this actually work so you'll need to use your imagination a bit here.
Step 24: As a finishing touch you can build a quaint garden next to your mill. If you're feeling up to it you could also start a great wheat farm next door.