Can a concrete porch be poured against a stone wall?
I agree with Tyler Durdens advice,with one important addition.
Don't lay your patio directly on gravel. Assuming your patio is about 75-100mm deep, gravel on its own will not offer enough support, and eventually, cracks will appear due to subsidence. A much better solution would be to "layer" your foundation in order of aggregate size.
Lay a layer (or two) of large stones,followed by a layer (or two) of medium stones, DON'T FORGET TO TAMP THEM DOWN!!!!,
followed with a layer of sharp sand,tamp down again,then gravel(tamp),then patio.