Start making the foundation by putting a wooden stick in the middle of the assumed slab.
Tie a 1.58m long string to the stick, by rotating it you can mark all the eight angles with the help of 1.21m long measuring board. Make sure that the length of the diameter is 3.16m.
The airintake pipe can be made from 4'' to 6'' plumbers pipe, and can be built into the foundation. One end under the grill, the other will exit the into the open air (preferably at the side of theBBQHut with the prevailing wind).
