Terracing a garden - where do I start...?

Our garden slopes upwards away from the house, and also upwards from right to left (so the left hand, back corner is the highest point).
What we'd like to do is terrace the garden into 3 levels:
top - circular seating area
middle - circular pebble pool/pond
bottom - circular lawn
with each circle being bigger than the one above it.

The gaps around the circles will become plant borders.

My question is: where do we start digging - which level should be done first?

Any advice & hints greatly received!

thanks

 

Hi ellgee,
This should help:

http://www.mastergardenproducts.com/gardenerscorner/terrac.htm