Hi Omar, it depends on the thickness of the card you are going to use for your 3 dvd disc boxset, but the measurements of one of my sets is… height is 190mm, width is 144mm, and the depth is 48mm.
I’d have a practice go first - or buy a cheap 3 disc boxset from a local market, car boot sale or a cheap shop - and have a play around with that to get it just right for the type of boxset you want to build.
Good luck 😃