You got any pics Parm?What type are you making ???
I've made a reverse flow off set smoker where the fire box and chimney are both on the same side. It's important to get the size of your fire box and air inlet proportional to the cook chamber and chimney size. I know this from years of experimentation/failure and success
Google Feldons BBQ calculator, it will be your friend in making all the calculations and finalising design.
I've now got mine licked! I use a 47 kg cylinder as the cook chamber and 13 kg cylinder for the fire box. I can get it to maintain a constant temp for around 20 hours for perfect low n slow ribs and brisket
Good luck