If you want to deal with variable size pathfinding nodes then perhaps it's worth looking into using Quadtree nodes for pathfinding.
now back to the problem at hand.
See the cliff at the left top the cell covers the top and the wall of the cliff how should I handle that sort of thing besides making smaller cells.
I want the units to go up there if they need to. thanks.
This isn't a completed algorithm (and it's not my video either) but this demonstrates the idea well:
This may or may not be helpful:
Essentially, from the sounds of it, you're looking for pathfinding on a variable-size grid. If not, then I can think of only two other options. Place custom nodes manually or make the grid finer.