The only ramp I have is 16 inches wide and measured out at an angle that makes it not so steep, we got a tape measure and held it from the pop door where the nest boxes are to the floor about 4 feet so the incline is more gradual. Also have 1X1 strips nailed across the ramp, spaced every 4 inches... for traction so that if for any reason they started slipping, they could get a hold on the strips. I had a 12 inch wide one first but found that they fought over who would go up or down more and always one got pushed off.
My 2nd coop has concrete blocks for steps up, and then the 3rd coop has a ladder with rungs...16 inches wide.
I like the concrete blocks the best because they stay put and seem to stay cleaner.