building shed base above soil

[adiwill]

Hi all, putting a shed base down on sloping soil. There's around 240mm of drop across 8ft. This obviously means i've got to build the base up from the lower end to the higher end. Soil is clay , so sub based definitely needed. I'm completely confusing myself with the best way to do this so would appreciate some input. I need quick and easy and want avoid concrete if possible, but realise this may not be possible.
Anyway, these are my current thoughts..

1) frame made of sleepers, partially filled up with sub base, compacted, then plastic shed base and pea gravel level to top or sleepers.
2) Sleepers Frame, sub base level to top of soil, then 240mm of concrete level to top of sleepers
3) Side walls made of pavers dug in and cemented in, sub base, then leveled to top with concrete.
4) Timber frame, sub base, leveled off with concrete, and frame then removed.

I'm favouring number 1 (sleepers, sub base, and plastic shed base/gravel) for ease, but once the sleepers start rotting i'm concerned the compacted sub base will then shift or just fall apart. I know that may take years but it's still a concern.

Any advice or suggestions?

 

[motorbiking]

2 options:

1. Build a frame that is level on posts that you can postcrete in. As if building a decking. This has the advantage of allowing air flow.
2. As above but use shuttering and concrete or simply fill with gavel (needs more solid base).