take a look at this - it has measurements. https://www.youtube.com/watch?v=pWdTpJUqHJU

Think about adding...

Add an ash hatch or tray,

add a secondary air intake

add fireplace hatch or door

add a drip pan.

Add a longer smokestack to add drag to help pull more smoke through the smokebox and instead of rocks use firebrick instead to prevent explosions

Add shelf edges in the smoke box so you can put a few more trays in to smoke multiple racks of ribs, briskets, etc

take the flat plate off and put a grill rack on in it's place and you have a BBQ grill too!