I have an area at the back of the house that I am going to concrete, its going to also have a retaining wall(small one) at the back of the slab. I haven't do it before but have the father inlaw coming up for the weekend, and he has done a few before. What I wondered was how thick should I make it? no vehicles. Reo? Also how level does the site need to be? and if I need to fill should I use blue metal? What is the cheapest way to make the boxwork, ie, what type of wood and thickness. Thanks...

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