Build A Wind Turbine or Buy One?

Building a wind turbine does require a certain amount of technical and practical expertise. Assuming you haven't built a wind turbine before you'll be looking for some technical expertise and practical guides on building wind turbines.
The three areas you will need to know about are -
Electric Demand - This is the amount of electricity you are using and how much of this you wish to provide from your wind generator. Depending on how much electricity you require will dictate how big a system or what percent of your electricity can be provided by a wind turbine. (If you are not already using energy efficient products you may be wiser to start spending money here first!)
Electrical Wiring & Storage
If using anything other than a 12 or 24 Volt electric system you are advised to have a qualified electrician either install or check your system before use or even during the design process. Even if you are going to be using a low-voltage system it is advised to have an electrician check your work.
Assuming the wiring is understood and planned the next thing you need to consider is storage. As your electricity use and available electricity from your wind turbine will rarely, if ever match, you need a storage system. Your electricity usage requirements will be a large factor in deciding on how big a system you will need. Electricity storage of wind power is a factor that many do not plan for or budget for when first considering the use of a wind turbine. Some people even make the mistake in thinking they can use cheap auto batteries from the breakers yard rather than the the much more appropriate deep-cycle batteries. (This is covered in more detail below)
In reality a suitable electrical storage system for wind turbines can cost almost as much as the wind generator, or in a home built wind turbine system it can be as much as 90% of the budget.
Alternatively some people are in the lucky position that they do not need storage as they can actually sell the surplus electricity back to the local power company. Though the additional equipment you will be required to install will likely cost as much as a bank of storage batteries. You are unlikely to have this option from a home built wind generator, and in some countries it is very difficult to obtain an agreement to sell your surplus electricity to the electricity company. (more about this below)
Designing and Building a Wind Turbine -
To generate a useful amount of electricity from a wind turbine you do need to be seeking expert advice on the design. Considering the time and effort spent on building a system you do want to be building the best design for your budget and needs. The pitfalls of pennypinching or taking shortcuts at this stage could mean a system that provides no or little useful power. Also, if the wind turbine is badly constructed it will only last a very short time before failing and it could even become a serious hazard to persons, property, pets and livestock depending where it was situated.
Rather than link to websites here that offer instructions for building wind turbines though often details are sketchy, incomplete or missing entirely these books are highly recommended.