Get as many options, bells and whistles the above have mentioned. Must consider where and how the pit will move from the delivery truck to your intended location. You'll need 8" wheels, a few thick plywood boards to lay down across the lawn, and additional muscle to guide. The pit in question will be in the neighborhood of 1,000 lbs.
24 X 48 chamber, 1/2" firebox (will add significant weight and heat retention properties), side vertical chamber, sliding shelves, ball valve.
Enjoy for many many years.
Cooking at Mason-Dixon BBQ Services
Lang 84 Deluxe Kitchen known as "The Glamazon" , Custom Klose Backyard Chef... of Snot, and a 22.5 WSM
Lang 60 Mobile - The Damsel II, Lang 48 Patio - The Damsel, Bubba Keg Grill - RIP, Double Barrel Smoker and a BSKD