Head to Home Depot blackcats and get one of their cement mixing tubs. If I remember right they are under five dollars, very sturdy. We have a Mainecoon cat that's rather big and all normal sized litter boxes were too small for her.
I sure wish the cat industry would realize there's a need for larger litter boxes. I would really like a large one with the sifters in them. My Mollee refuses to use it. Good thing we have two litter boxes. I do believe I'll have to go back to both being the cement tubs though.

Here is a link that might be useful: {{!gwi}}

Oh thank you!!! That is a great idea! I'm going to get 2 tonight and set them up.

I'm so glad I could help a fellow cat lover!

This may be way overkill for you, but I'll share it anyway! I lived for many years with a male cat who was initially prone to bladder/kidney infections, and later, diabetic. He was very picky about the cleanliness of his litter box, and given his urinary disabilities, I went through a lot of trial and error. What worked best was the Rubbermaid under-the-bed storage box for rolls of wrapping paper -- huge, but it worked! Fortunately, my mud room had space for it! It was large enough that Smudge could always find clean spots and it absolutely solved both problems: his "Not clean enough here, so I'll just go somewhere else" one and his "Oops, missed the box" one.

Despite his health issues, and the hexes my DH tried to put on him, Smudge lived to the ripe old age of 19!

Let me offer a little advice, been there, done tthat, don't get one of those covered litter boxes with a "hood" over the top, they look like a plastic igloo. My cats (well, two out of three) refused to enter it, I took the lid thing off and threw it away.