Well I an now of and running (hopefully) with the completion of my base. The sure had a fall of about 180mm. Hence why it is at such a jaunty angle. Used some cinder blocks, bricks and other aggregate to in fill somewhat and then poured the base using self reinforcing premixed bag cement.
Thank goodness for cement mixers, 20+ bags would not have been fun.
I am aiming to complete the task, after being challenged by my good lady, for $500 nzd or less. Thus far $185 spent on concrete, bought my bricks and refractory bricks for $1.50 on trade me, so on track to make budget. Oh just found a load of reinforcing grid and timber for nicks from a neighbour clearing out his garden for spring
Will keep watching your posts and I'll update add I move along the project.
Any pointers or ideas or things I ought to consider are gratefully received