I had a ramp put on my two horse straight load trailer. I went to a welder to have it done. It was a metal frame with wood insert (made out of a heavy plywood sheet) for the horses to walk on for the inside (closest to trailer when in travel position) and an aluminum (I think) sheet on the outside plus a bit a bumper welded on the bottom. The frame had about a 2 inch lip and was welded around the wood and aluminum after they were cut to size. I later added rubber matting to the wood to give more traction. I`m sorry I don`t have the measurements handy but it was a few inches wider than the door opening and it was longer than what you see with built in ramps (my guess is it was 4 ft long when most built ins are 3 ft -- that sort of difference). It had to be longer as it was welded on top of the trailer`s existing bumper and needed the length to slope to the ground. The ramp was secured in travel position by threaded eye bolts run through holes made in welded on plates. You needed a good strong back and legs to lift it one go.