The Windmill requires you to collect quite a few items before it can actually be built:
- 7 Metal Blades
- 7 Wooden Trestles
- 7 Drive Shafts
- 7 Spur Gears
- 7 Weather Vanes
- 7 Small Pumps
The Drive Shafts and Small Pumps are found almost exclusively on Expedition maps (you can click on them within the Windmill's menu to be taken to the appropriate maps), while the other four items can also be earned by asking your friends to send them to you.
Once you've finished building the Windmill, you'll be able to tend it once per day using Supplies. The first day that you tend your Windmill, your maximum energy cap will increase by +1, and you'll need to keep tending it once per day to keep it there. Likewise, if you forget to tend it for a full 24 hour period, the cap will drop back down (but can never go back below 30 points). If you're familiar with the Dam in CityVille, this feature is incredibly similar in that respect.
You'll need to upgrade your Windmill by collecting more and more parts, so that you can eventually reach Level 4, and have the most room for improvement. Level 2 will allow you to reach a maximum energy cap of 34 points, and Level 3 will allow you to have up to 38 points. Level 4, of course, finally raises the maximum allowed energy to 42 points. Again, you'll gain a point each day that you tend the Windmill, so long as you continue to do so without missing any days.
Will you try to upgrade your Windmill all of the way to Level 4, or are you fine with just having 30 points of maximum energy? Sound off in the comments.