While the concrete was curing, I cut and profiled the main timbers that form the corner posts. Each post is a 100 x 100 mm treated softwood fencepost with a tapered cross-section strip fixed each side to take the external cladding. You can see in the image above a bolted hardwood block on each post, which supports the perimeter floor beams. A similar hardwood pad was fixed to the bottom of each post to resist rotting from the damp ground.
Here you can see the posts fixed into position. They are not fixed to the ground, which retains the “temporary structure” nature of the building - helpful for planning regulations and also good if you ever want to move it to another location (I guess a big crane would be handy!)