Good post above.
Basically are you talking about a temp or permanent pit?
Temps are usually smaller and shallower, and often filled in at the end of the day. Best to ask the farmer fisrt, as in years past when they had smaller dia tires, they could break the axle if they hit the old pit even when filled in.
As for Permanent pits, there are concerete, wood, fiberglass, plastic ones. They basically use a back hoe to dig them. Most are about 5' deep. Basically so a 6' man can sit on a chair and his head is a few inches below the top of the ground.
The ones I have hunted out of were wood frame, 16' long, x 4' wide and 5' deep. Often a"flop" top is used where you flip the lid behind you and then fire. The lids are made of wood frame and chicken wire so the vegetation can be woven into the wire, and also allows you to see out between the vegetation which is important when calling geese and ducks.