Depends on the species on how big they will get. Also, the height of the tank is a good point, a 20 gallon extra long or a custom tank that is only 10 inches tall and maybe 40x30 would work really well for them. I know it is more expensive if you don't make your own but the total floor space will
could be more important than the total gallons. I have seen figures on this but I think 1.5 square feet for each craw if they are larger species or 1 square foot for smaller ones. The key is they need to be bale to hide so they can not see each other if they don't want to.
My local fish hatchery raises them in a "runway" that is 15 feet long and 4 feet wide, they have diciders in there and a lot of pvc and rock caves for them to hide in, they even breed in there. I think any tank that you can provide a good, "comfortable" place for them to live in will work, just make sure there isn't any aggression and if there is make more hiding places.
If you are talking baout a single one then go for a 10 gallon. I have never seen one over 5 inches long so they should work well with good filtration.
Most important thing to remember, they are escape artists and will get out if they have any way to do so. Even if you think a plexi top covers the tank, make sure it is secure. I have seen them move rocks the size of baseballs, the wild ones anyway.
I do stand corrected, I found a couple species that get over 12" long, that a lobster baby! Anyway, HERE
is the only descent link I could find. There is a much better one but I can't find it for the life of me.