First of all - you have to go here
and check out this amazing Instructable!
I looked at this and thought it was good enough to make but I couldn't see where I'd store it when not in use so I made a de-mountable version of it. To do this I made it in sub-assemblies and then bolted it together.
You will need, as stated in the original, lots of cardboard (we've just moved house so I had the luxury of picking a big stack of identical strong boxes), Sanley knife (box-cutter), hot glue gun, rulers, pens, etc. and then as well, lots of nuts, bolts and washers. We went through nearly 60 nuts and bolts and 120 washers.