Have a look at this old pit that has been in the family for many years.
At first the fire box was on the same level as the cooking chamber. The only way into the firebox was from the top. At some point my dad and/or brother decided enough was enough and had the firebox lowered, a baffle installed and the door moved to the side. Much Mo Betta.
I think the firebox could have been lowered another 3 inches.
I also like the idea of a flat surface on the top of the fire box.