I have a 3 sided shop bldg., 36'x30', with dirt floor. It has 3 12' bays, which I will eventualy get around to pouring a floor, probably one bay at a time. I put up track under the front eve, and am in the process of building 3 sliding doors to enclose the front. When the weather warms up some, I would like to build a masonary chimney in the middle of the center bay, for a wood stove. I am sure that a concrete base has to be poured first, but don't know how big to make it, and how deep. The chimney won't be over 25 ft tall. I have never seen the chimney materials, nor watched one being built!, however I am imagining rectangle concrete blocks, with a 8" hole in the center, that just stack up , with morter between. Is this accurate? Some one please enlighten me!