I had to tackle this recently so I did some research of my own: came across this handy article that has some informational photos:
How to Walk on a Concrete Tile Roof | Lyons Roofing Blog
Here’s some info from the post:
“Most concrete tiles are lifted a little off of your roof and sit on wood batten strips, creating a gap under the tiles for ventilation. When you walk on your roof, make sure you are walking on the reinforced part—the lower third of the visible tile where tiles overlap.”
“Also, walk on the peaks of the tile, not the valleys.”
Hopefully that helps answer some questions for people out there. I’m paranoid about cracking tiles as that could be some water damage down the road for your client.