One thing to be wary about with the '4U' cases out there - while they're all the normal 4 rack units high that the name implies, if you're thinking to put them in a normal data center rack, most of them are NOT 19" wide, the size of a normal server case. For me that's not an issue, I just designed a rack to hold them, but be aware that it can be a bit confusing how they call them rackmount servers, but you'll need to get a rack that is adjustable to support their non-standard widths.
Thank you for that information, did not know that!