I've heard that they don't grow fast as compared to other catfish. Are you asking what size tank for a full grown Lima? If so, assuming that 20'' is a reasonable full grow length, I would say a 24'' wide tank at a min. A better sulited tank would be 36'' wide. As for length, I would do 72''. This is all my opinion. I sure others will have different suggestions.
On a side note, I'm thinking about getting 3 Limas for my 96X36X36. I think 3 of them would look sweet in there.