Though I'm sure no one will believe me, I was thinking about building a wagon before Paul posted his. Here's my take on constructing an early mediaeval ox wagon. This is the first part of a set of builds I'll do to get the three wagons I need for Dux Brit wagon train scenarios.
There's a full build how-to on my blog here:
http://mitchwargaming.blogspot.co.uk/2013/09/wagons-roll-part-1-two-wheel-cart.html(warning, it's picture heavy).
Here's a shot part-way through construction:
and here's the finished article: