I'm no expert at this at all, but am astounded that one would undertake such a project without prior knowledge and planning. The risks of doing this incorrectly are considerable. If it were me I would meet with a mason that I respected and pay him as an adviser if need be. There are several important steps in this process including the foundation pad be appropriate for the soil type and height of the chimney. Then there are clearance issues and proper sealing and caulking to be considered. As for the thimble, the rules are pretty clear. It needs to have the proper clearances from combustibles in all directions.
This article should be helpful:
https://www.hearth.com/econtent/index.php/articles/installing_a_woodstove
Masonry Chimneys
The details as to the building of masonry chimneys are beyond the scope of this document, however there are a few safety and performance issue to keep in mind. It is commonly known in the Hearth Industry that 80-90% (or more!) of the masonry chimneys in the US are constructed improperly. The sad truth is that some masons spent so many years building low-temperature chimneys for oil burners, gas burners and fireplaces that the art of proper chimney construction has become almost lost.
What’s wrong with most masonry chimneys ?
* They are often oversize and not insulated, resulting in poor draft and excess creosote formation
* Proper clearances to combustible (wood framing, siding, etc.) are not maintained
* No room for expansion of the flue tiles, resulting in cracked and damaged liners
These deficiencies can be addressed during new construction by a competent mason, and a properly designed and built masonry chimney is a work of art that can last for generations. An existing (but deficient) masonry chimney can often be brought up to spec by installing a UL approved stainless steel liner system. This provides an extra margin of safety as well as improves draft and simplifies cleaning.
For the proper information on building masonry fireplaces and chimneys, see the links below:
(broken link removed to http://www.gobrick.com/BIA/technotes/t19b.htm)
(broken link removed to http://www.maconline.org/tech/construction/chimney/chimney.html)
http://www.bia.org/html/fireplace_and_chimney.html
Things to Remember about Masonry Chimneys
* The flue liner of the chimney should be the same size (or just a tad bigger) than the stovepipe size,
* The chimney should be located inside the building if possible, and insulated (with vermiculite or other masonry insulation
* The flue liner should be either a “cast-in-place” type (ask your hearth dealer) or other form of constructions which allows for expansion.
* Most existing masonry chimneys need to be relined with stainless steel pipe