Laying the decking directly onto gravel is not really a sensible approach as the frame will want to expand and contract (like all timber does) which will make the whole section move. It may also warp and rise off the ground in one or more corners as there is nothing to tie it to the ground. Correctly structured decking platform does not touch the ground, neither do the beams nor the joists… even with the best intensions in the world if you want a structure that will last then you should really commission a designer or take a look here https://deckingnetwork.com/decking-substructure/
This is a basic advice page on how to create decking structure… We can advise but only so far.
What decking brand are you considering using?