Something I did for a ramp. I used two wooden poles, as long as you need them to be. Cut a piece of chicken wire the same length but a little more than twice the width as you require. Now lay the poles on top of it. Place a good thickness of straw between the poles. Now fold the remaining piece of wire over and fasten it with a piece of wire, or bend the ends to hold it together. Now, so that the chooks don't get their little toes stuck, use pieces of wire to bring the wire on the ramp together in places (from underneath). This will make the straw tight between the wire and strengthen it. And there you have it!!!!
Another idea is to join twigs laying around the ground together to make the ramp. Cheap and inexpensive.
Hope this helps as one idea