By inrun you mean ramp yeah? Mines basically the same as your description (2m tower, 1m square).
My advice would be to start with the angle you want for the ramp and attach a sheet of ply to 2 2-3m sturdy pieces of wood. You could probably fit a whole sheet of ply flat on the ramp then another curved for your transition.
you cant just use plywood your gonna need some wood underneath. Framing lumber comes standard up to 16 feet and usually longer. So that wont be a problem. When you lay down the plywood it wont matter if there are some seams. If you are worried you can run a cross piece at the seam.