My favorite smokers are set up on what we call the reverse flow design. With this design you do not have to worry about flare ups burning your meat. I used old propane tanks which I buy at scrap prices - about $25 - $50 apiece. Whats so nice about these tanks is they are made out of 3/8's inch rolled sheet metal and they really hold a constant heat. Once you get the grill set with the dampers it will hardly budge off the target temperature and all you need to do is add about 3 sticks of wood every hour and the smoker does the rest. You could add a rotisserie but it really is unnecessary with this setup.
Here is a general schematic of the setup.
The solid plate is the key. I use 3/8's plate for this too to insure heat but the main heat and smoke rolls under the plate and then up through a gap at the far end of the firebox then the heat and smoke flows back over the meat and out the chimney. In this design, there are no dampers other than at the firebox and everything is controlled from here.
Here is a pic of the firebox on mine. If you look at the upper side of the firebox you can see where the heat and smoke enters under the plate. Each smoker is uniques and has its own sweetspot. This smoker likes to be run between 250 - 325 degrees.
In the grilling area I have three racks for cooking. These racks are held in place with C channel in a drawer like fashion except the bottom racks. All can be removed or adjusted depending on what I'm doing.
Here is a pic of some turkeys I cooked for Thanksgiving. I removed the third rack and have them on the second.
Here is a smoker/grill I made this summer. My objective for this grill was to lower the sweetspot and create something I can smoke sausages with as well as BBQ other things. I built this one out of a 250 gallon propane tank and a 125 gallon tank mounted vertically for sausage and hams.
Unlike the other one, this one has 5 dampers to control the air flow into the different chambers. The sweetspot on this one is 225-250 in the large chamber and 125 - 150 in the vertical. (simultaneously - I can cold smoke in the vertical alone)
Here is some summer sausages in the upright
I'm not an expert on this stuff by any means but I have learned a lot of things not to do on my next build and some things to watch out for. Before I started tinkering with this I was clueless to all the science that goes into making one of these things. But with the right instruction - they are not hard to build at all. Key is to start with a good plan and some good help and some patience. Hope this was helpful and gave you some ideas.