Lucky for us the government is keen to encourage individual builds. This means as well as designing a house to your own specifications there is also a nice surprise when you consider you only pay stamp duty on the plot price. For example (in England) if you purchase a £200,000 plot your stamp is £1500, the finished building is likely to be around £600,000, if you were to purchase this as fully built house your stamp duty would be £20,000. A nice £18,500 saving
Purchasing as a second home, the stamp on the plot would be £7500 and purchasing the finished building would be £38,000 saving you £31,500.