Mine will not be a "suitcase" but same concept, and luggable. My experience with plastic cases has been bad, unless you're going for very small battery capacity. I'm contracting out having an aluminum box made to my specifications.
There are premade aluminum cases out there. Check out the "Alu-box" line. That was my plan B if I couldn't get a custom case.
If you're going small, then the options broaden up considerably.
Pick out your parts, lay them out in Sketchup to get a sense of what volume you need, then go case shopping once you know your min dimensions.