I,ve built quite a few out buildings, and find that this spacing works well, and takes the weight very well too. As long as it has bearings underneath, that helps alot. The wood is treated, and i will be putting a dpm membrane on the whole underneath to prevent dampness. The sides will have the membrane on them as well, and the roof will be pitched, with a heavy felt on and strapped down to protect from the strong west wind that i seem to get hit with now and again. I have creosote and old engine oil that will be applied to all wood liable to be hit by weather, so all in all, making sure its done correctly from the start, and to last. Thanks for your advice ian.

alex