How create a manually or custom navmesh geometry to enemy works good?

I need create manually custom navmesh cause bge auto not working good not work correctly with ground are in up is a plane not in 0,0 position with objects around.
I try create a plane extruding faces and when put for navmesh only quads all chequed with ADDon mesh faces select and start P few times after blender 2.79 close all.

Please help me

I just remmember the blender have power for model and navmesh with extrude verices we create a model, i just work with quad faces only and with attemption to lost vertices in extrude can cause error on navmesh.For working the enemies with dynamics phisics steering pathfollowing working fine.
Obs: all time you edit the navmesh reset all data in properties.