I made one years ago out of 36 cynder blocks and a tin roof to roast a whole hog in and it worked perfect.
4 blocks long
2 blocks wide
3 blocks tall
Grate between 2nd and 3rd block and a sheet of tin roofing for the top.
Built a fire on the outside and shovel hot coals in each end as needed.
All the nay sayers said the blocks would get hot and bust but i did a whole hog once a year for 3 years and never had a problem
Turned it in to a permanet pit mortered all the blocks and filled the holes with cement built a top out of sheet metal and a fine paint job.
Had a many nice smokes out of that pit then the ex wife got the house and the pit in the settlement.
"Boy I sure do miss that Pit."
I have a couple pics of my last whole hog party.