For me; first head size and then shell depth works best. I don’t know, maybe it’s because i’m dutch and we use a different metric systeem, centimeters instead of inches to determine the size or depth, or lenght for that matter.
I know what size of toms and basses i want on my next kit (when able to buy one ), i only have to think and decide about the depth. That’s still a tough decision to make, but i have some time to think it over, more time than money.
But maybe in the end it’s not a very big deal, if all the drum fabricating companies would use the same system, then all i have to do is get used to whatever they will decide.
Head size - shell depth is what i know now, shell depth - head size, i need to keep in the back of my mind when i will buy a new kit.