New shed on seriously poor concrete base

[UnusualCapybara]

We just demolished an old tin shed and what lies below is an extremely unhappy concrete base - some pics attached for amusement.

The plan is to self-build a mega-shed/workshop (approx 10M x 4.5M) on a timber frame but the levels in the current concrete are so poor it's not usable as a base. I think my current options are:

1.) Drill down into the existing concrete base in a number of locations to install legs or piers which can be individually levelled.
2.) Shutter the existing concrete area and do an additional pour on top to bring to a level.
3.) Try to get the new floor frame level by some combination of propping up with bricks/shims in the low spots.
4.) Something else I didn't consider yet.

The site is at the end of a ~100M garden with no road access for concrete so anything involving breaking up or even pouring more concrete is low on the agenda.

Any advice welcome!

 

[Deluks]

Doesn't look too bad for a shed.
How thick is the concrete?

Will your new shed have its own floor or is this going to be the floor?

 

[big-all]

do you have planning and building regs permission ??

 

[UnusualCapybara]

Doesn't look too bad for a shed.
How thick is the concrete?

Will your new shed have its own floor or is this going to be the floor?

The existing concrete is 80mm thick but the level is all over the place with a 35-40mm drop in height in some areas due to cracking/splitting.

I had planned for the new shed to have it's own timber floor structure so it would just be a case of getting this new structure level.

 

[UnusualCapybara]

do you have planning and building regs permission ??

Not yet, I only finished clearing the old shed yesterday so I'm still working out what I'm going to build but I'm aware that at the dimensions stated, I'd need planning.

 

[Deluks]

If it will be a timber floor then airflow underneath will be a huge benefit.
You might as well raise it up on timber sleepers, concrete blocks or stacked paving slabs. Stiff mortar bed underneath, strategically placed, to get it level.
The existing base should take the weight if there is enough support to spread the load.

If there is considerable movement in the ground (on clay? Near to large trees?) then you may have ongoing problems. But if you make the shed base stiff enough you might get away with it.