Incidentally, the gravel base assists drainage, but its primary purpose is to provide a solid, unshifting base once the walk is tamped in. Since we can't see and handle the gravel you're talking about, it would be impossible to say if it would work, The gravel needs to be crushed, with all sizes ranging down to sand and dust. The river gravel is likely rounded. It might work as filler for the lower portion of the base, if it is mixed with enough crushed material.

If by paving stones you mean interlocking pavers, then no, for the reasons Yard stated. If you mean big slabs, *maybe* it would work if the gravel was angular. If it's rounded (as Yard suspected, and that seems reasonable), imagine a piece of plywood on ball bearings and you'll have an idea of the suitability.

The contractor offer to made the paving (Cambridge stone?) with the foundation under paving as a concrete slab 3-4" thick, then layer of sand and paving stones on top. The area of paving is about 25'x10'. Is it how it suppose to be made or that foundation with layer of concrete is not necessary? Or (like in the neighbor's house) is it enough just to have the layer of compacted sand on the top of the dirt without a solid foundation?

What is your soil like? I live on sand and I like a concrete base to stabilize the area.

I don't know for sure, probably sand (Long Island, Oceanside, NY). My question actually was driven by my point of view (maybe wrong?) that the base should be porous enough for good drainage. The concrete base obviously will not provide proper drainage while give a good stable surface.