My husband and I are getting really close to becoming cat owners. One of the things I needed to get done to make the house cat ready was to make room for a kitty litter. The toilet paper was on the floor were the litter box is. I used the utility door as a guide for the shelf height. I lucked out in that being exactly the correct size for the TP.
I measured the length for the 1X4. Cut with a circular saw. Pre-drilled holes for the screws in the wall, while making sure it was level. Then we secured it to the wall with 1.25" screws. To make sure the shelf would be level across we measured the distance from the floor to the bottom of the wood, and then marked it out on the opposite wall. Then repeated the steps for installing this shelf spike.
I used the scraps from two 1X12s, and measured the distanced across, and then cut them down with a circular saw. Then simply plopped them in place. It works perfectly. I suppose I should paint them white like the other shelves, but the bare pine is attractive for now.
I can't wait until we become cat owners. Hopefully after the holidays! Happy DIYing, chris!