Levelling slope with decking

Any ideas where to start for decking on a slope? The base is loose stone and what looks like crushed hardcore underneath. The goal is to level with decking and build a shed onto the rear towards the back of the decking using the house as one of the walls

How should I start with the base? Will I need to remove stone topping, drill and pour concrete for adjustable decking risers? Or is their an alternative?

Link to image
https://m.imgur.com/a/EG06d2H

Thanks.