Most editors can set the offsets automatically, but WadEd can't, so I have quite some experience of this :)
All the lines are offset from left to right, so start with the side of your stairs that starts from left and up, then goes down. You didn't say if the lines on the side of the stairs are one sided or two sided, so this is the case of 1-sided linedefs.
The first line, if the ceiling also goes down 16 units, has to have an Y offset of 16, so it's moved up. If the ceiling height doesn't change, there is no need to change the Y offset. The second line, if the lines are all 64 units wide, and the texture is wider than 64 units, has to have X offset of 64, and 16 more of Y offset if needed, so it's 32. The third line's Y offset should be 48, and If the texture you use is wider than 128 units, X offset should be increased by 64, so it's 128, and so on...
mirror the Y offsets to the other side of the stairs, and align the X offsets, starting again from the left.
I hope this makes some sense, it sounds more complicated than it really is when one gets the hang of it.