I've seen that even the cases supplied by the factories don't properly support the guitar.

Fender-type guitars, with the fret board parallel to the face of the body, need to have the neck supported at a higher level than the back of the body.

Les Paul type guitars, with the neck slanted back from the body, need to have the 'floor' of the case, and the neck support, match the neck-to-body angle. Too often, (more like always :p ), the neck-body joint area is unsupported.

Add in weather resistance, shock & vibration isolation, low weight, and recessed latches & handle, and you soon see that a properly designed case is a sophisticated balance of potentially conflicting requirements.

And speaking of balance, make it so a loaded case is comfortable to carry, without doing unkind things to your wrist!