I would consider 50' the minimum comfortable width. I have a local airport that is 35' wide that I use but there is no room for error. You must maintain centerline. Even if you touch down on centerline there is always the issues of maintaining control till the jet stops. My A-4 for example is a very squirrelly bird on the ground due to the narrow wheel base. Not all would agree, but if I were building a runway it would be a minimum of 50' X 1200'. And at 1200' long I would need a clear, flat, long open approach path that would enable me to touch down in the first 25% of the runway. I know I am spoiled by my 75' X 5000' runway at my normal flying site but hitting a 25' X 400' runway would not only be impossible for me but certainly not worth risking my expensive jets. I tend to fly heavier scale jets so that is why I have to travel 200 miles one way to fly on the weekend in order to use a suitable runway.