Thanks to Tim Crump for the following tit bits. Oak trees are harvested at around 80 years old. Each one will produce around 15 ft3 (cubic feet) of construction grade oak. The typical oak-built family home uses 800ft3 of oak, the produce of around 50 trees. Almost all the oak used in British green oak homes is sourced from French and German plantations: English oak is available but it’s more costly (at between £600 and £700 per m3, as opposed to £500-£550 per m3 for Continental oak) and it tends not to grow so tall and straight which makes it more suitable for furniture than construction. The species is identical.
Finally, there 35 ft3 in a m3, so a 50-oak tree house has £12,500 of oak going into it.