What's the footprint of the tank? And how far below the highest drain point is the lowest thing that leads back to the sump? This usually means what's the height difference between the top of the overflow and the bottom of the return line. That determines how much water will continue to flow into your sump after the return pump stops.
Typically, you don't need (or want) a sump that's too deep (i.e. too close to 28" high) because it makes it hard to work in the sump for cleaning and moving things in and out. In your case, I wouldn't go over 20" deep and get as big a footprint container as you can find. Any aquarium, Rubermaid tub, or other food-safe container will do the trick. At 24" in length, standard aquariums are going to be somewhat limitted to 20 high and 15 regular which are only 12" wide and 24" long. That will make for cramped space for a skimmer. I think you'll be able to find Rubermaid tubs with greater widths.
