My condolences Morana, gravel
sucks. About 8 inches you reckon?
I'd be worried about potential garden health issues if there's not much in the way of actual, mineral soil.
So while I think well aged chips, with a
lot of nitrogen (urine, grass clippings, used coffee grounds) to deal with the carbon would be great, I'd also be seeking soil.
Maybe craigslist, that truck, a few workers and the promise of beer...