I have used many different smoker designs from a tent of fresh cedar boughs (taught to me by an old friend, Chief of the local First Peoples in my home town), to a plywood box over a buried Hibachi BBQ.
My current smoker from the last 25 years kinda sort of resembles a pellet BBQ without the automation. It was made from an Aluminum barrel keg (residual from my last grad school kegger party) and a discarded stainless wet sink (from a previous semiconductor employer). I had some mech techs help me clamshell the keg and build a door for the firebox (sink). The firebox is connected to the main chamber with 2" pipe and fittings to bring the smoke sideways from the firebox and underneath the racks to provide a cooler smoke for slow cooking.
I use this keg setup to smoke fish, sausage, brisket, pork shoulder, ribs, and turkey. Sometimes cold smoke, but usually just indirect heat kettle style.
A very versatile BBQ smoker.