My case is too big, it’s an Antec P280 .
I had to get longer power leads for the disks and there’s a lot of empty space.
It stick out from under my desk an inch or too also.
It’s a good case though, quiet, lots of fans and well built, it was easy to work with.
If you start with the size of your motherboard, add a PSU and disk drives, and the most humongous heatsink you can find 
,
you’ll get an idea of the size of the case you need.