I know jb asked you alot of questions, for a reason!
It is important to know what climate you live in as to the frost depth. It is important to know how big the roof structure is going to be for weight calculations.
No one here can tell you how thick the cement has to be with out the answers. You need to be below the frost line.
I know you don't want alot of holes in the ground but, they are only holes until you fill them.
You can rent an auger from a tool rental store and insert the sauna tubes and your on your way.
Please post back and we will try to help!
© 2017 Renovate Your World LLC