There are a number of materials suitable for building a ramp. The height difference is one of two parameters necessary to determine a suitable material. The other parameter is often called the "run." In roofing terms, it's rise over run. For the purposes of this discussion, we'll consider that you have only reasonable limitations on the value for run and ignore it, more or less.
One must expect that the ramp will take force from a human being stepping on it, which eliminates a hollow design using, for example, cardboard.
Modeling clay which will harden over time may serve your requirements. A generic term is oven-bake clay. The material would be shaped to your location and heated per instructions. It may require reinforcement within the material, akin to rebar for concrete. This could be fine wire mesh, perhaps 6 mm / 0.25 inch spacing.
Another option is stacked flat solid material. Many options here, such as linoleum tile. The first layer encompasses the entire width and run, while the next layer is a few mm shorter in the run dimensions. Each subsequent layer is shorter by an appropriate amount until the top layer mates with the higher surface.
With a material such as linoleum tile, one can contour the edges to remove the abrupt transition, but it's likely your machine can handle the minimal jump of a suitably tapered stack.