Cases like these can be bought at webshops, some examples are :
- http://www.grovemade.com/product/iphone-5-case/#plain-bamboo-iphone-5-case (79$)
- https://www.miniot.com/webshop/?portlet=miniot&page=iwood5&state=maximized (79$)
Just as much as the iPhone is a precision device, manufacturing this case will require precision.
Apart from that, with basic tools and very little materials, you can build a really impressive protection for your phone.