Levelling shed base

[Stringman_uk]

Hi All
following on with my multiple posts regarding building my summerhouse.
Foundation is done and the base (4.6m x 2.4m) is built.
When I laid the base there are a few of the foundations ( compacted MOT1 with cemented flags on top x 12) where the wood is not touching
If you stand on the wood it then sits fine.
the slabs are all level so I suspect the wood is a little warped .
Should I ignore this and hope the weight of the walls etc flatten it out?
Or should I shim the bits raised?
If so should I use the plastic shims that you buy in screwfix of use some slate or other thin material.
The biggest gap is around 12mm.

Thanks

 

[JohnD]

Is the wood in direct contact with the damp concrete?

 

[Stringman_uk]

Is the wood in direct contact with the damp concrete?

No its not, the concrete has a dpm fitted.
Any thoughts on the original question?

 

[Mr Chibs]

Turn the wood over so it's convex. Build your cabin, see what gap is left over and shim if needed.
The weight/wood may sag once built and it might not need anything.

A long crow bar will lever the house up enough to get a shim in.