So, when creating an AImesh, which is better to use Stairs or Ramps? Ramps can be a lot cleaner and easier to implement, It would seem to make sense that ramps would be easier bot to use as well. After all, ramps have a lot fewer faces, so they would be simpler and less likely to have any mesh issues.
However it turns out that the navmesh process works better with stairs than ramps. Ramp navmeshing is inconsistent. Stairs actually navmesh much more reliably. Steep stairs will also work, where a steep ramp might not.
A lot of times, the col2 can be cloned and cleaned up a little for the AImesh and it may have ramps. The col0 will have stairs, but it is usually more complicated overall than what is needed for the Aimesh. One way is to use the stairs from the col0.
To start, make a clone of col3 and then delete all the mesh except to the stairs. Clean up the stairs and then export to 3ds format. 3ds format is a generic format that keeps the size and position information, so it can be imported back into the scene and attached.