Please note that advice given here must be adjusted according to the ground conditions and undulations on your particular site.
In general log cabins do not exert tremendous loading on to the base. The weight of the building tends to be distributed over a great length of perimeter wall. The majority of the foundation is actually supporting the floor alone plus the contents of the cabin, so very often the base is somewhat overkill for the internal loadings.
The best base is a concrete slab which is poured onto good sound ground or well compacted hardcore. The slab should be larger than the building by approx. 100 mm on all sides. It should be laid 100 mm thick or 100-150mm if the ground is undulating. Generally it is not necessary to include reinforcing mesh unless the slab is large and there is a risk of cracking. How to build a concrete base.
Alternatively the log cabin can quite happily sit on an area of concrete paving stones providing they themselves are supported on hard core or very sound ground. This does not tend to be a cost effective solution for large areas where the project becomes too labour intensive.