We were originally going to just repaint our bathroom door but after taking it off noticed one side was in pretty bad shape from the PO having a dog. I had taken measurements and seems like 24x72ish was about right. I found a closet door that was 24x80 and trimmed as much off the top as I could get away with and then took the rest off the bottom. Being a "hollow" core door I then had to take a stick of poplar that was a bit oversized for the core interior and jammed it into the bottom then glued and brad nailed it in.
Here is a youtube video very similar to what I did only its the side and not the bottom but both sides construction is consistent.
My original door was nearly 3 inches off the floor and this new one is more like 1/2"-1" instead.