Help with poured concrete outdoor rocket mass heater (with flagstone bench top)

I am looking for some information regarding the feasibility of designing a poured-in-place heating mass (in a 'c' shape) for a rocket stove heated bench to surround a proposed fire pit. I would have an insulated foundation on which the mass would be poured. I live in Ontario, Canada.
Thanks

Thomas Whitcroft : This is a good start, the Thread Extension posted by Erica Wisner contains much of the most important information you will need !

I expect this will be a hot topic ! For the craft! Big AL