How do I cut an old ladder to use as a shelf?

Lay it on the floor, measure between the rungs, if they are even on bith sides, make the legs even at the bottom.

I made one I stapled chicken wire to the back so things wouldn’t fall off. I just pulled it away from the wall till it was level This is mine. Good luck. The second one I used a whole ladder and anchored a support bracket on the back side with screws and glue

maybe it's not the ladder,maybe the boards are warped? add some shims under the boards to get them level use a level sitting on top to see how much or little of a shim you need

Cathy,

You may not have made your initial cut at the correct angle. If you just cut straight across, the rungs are now not parallel to the floor (front to back, not side to side). Have someone hold the ladder so the rungs are level (parallel) to the floor. Take a straight edge and lay it on the floor up against the side of a leg. Draw a line across the leg using the straight edge as a guide. Once drawn, you can move that line up or down to get the length you want. Now cut the legs at the angle the line is drawn at. This should make the rungs level.

Here is a post I wrote a while back on how to use a ladder for shelving >> https://www.homeroad.net/2013/10/ladder-shelving.html