You can make anything if you have the imagination and the tools. The longer the ramp the less steep it will be. It needs to be quite wide and have edged to avoid falls, and treads for them to grip to. I would suggest a scaffold plank, cut to size you need. Sand it to remove rough bits, pieces of half inch by one inch wood to glue on to the side edges, and nylon rope stuck in an zig zag to the surface to give treads. It will be quite heavy, so it needs to be secured at top and bottom. But, it is the only stable and long enough option to span the drop without being too steep.